This will not be your normal, run-of-the-mill review. In normal reviews, the product’s fully cooked, to the point where you can fairly evaluate every aspect of what the New Thing does.

Since this is a review of iOS 9, we’ll all need to wait a little while: it now transpires that we won’t be able to play with its star feature - 3D Touch - until the new iPhone 6s and 6s Plus reach UK stores on September 26.

For now, let’s call this review a work in progress: be sure that we’ll update it as soon as a 6s lands in the Stuff offices in a few weeks. That said, we have spent a full week testing it now on our iPhone 6 Plus 64GB. That’s enough time to know whether iOS 9 is a serious leap forward for the smartphone experience, or conservative refinement of an already successful OS. There’s certainly enough new stuff in iOS 9 to warrant anticipation among Apple followers - albeit some of it will be hidden under the hood for owners of pre-iPhone 6s devices.

Apple claims to have pulled off a trick that evades most upgrades in real-world usage: improved battery life (up to an hour more, they say, from a single charge) and snappier performance.

Even if you’re not upgrading to the new hardware, you’ll see above-the-hood changes from the iOS 9 update - the new Siri Suggests search screen (to the left of the main home screen, prompting parallels with Google Now), a new default font, hefty updates to several Apple apps and the arrival of Apple News.

The experience: iOS learns the search game

Truth is, most people upgrading to iOS 9 won’t notice a ton of difference. You will still, mostly, have the iOS interface you’ve known, loved - and occasionally been irritated by - for years.

No, you will not be able to move the icons to any point on any home screen (as you can on Android). No, you will not be able to pop widgets on to any point on any screen (as you can Android). It was iOS, and it’s still iOS.

But unlike previous iterations, there’s one enormous difference. Swipe to the left from your normal home screen, and there’s a Siri Suggestions screen. By Apple standards, this is a revolution on the scale of the fall of the Berlin Wall. A whole new screen. And you can’t put icons on to it. Lord save us.

Time will tell just how useful the world’s iPhone lovers find Siri Suggestions. The good news is that it’s nicely designed, and works. If you want to find something fast, type or talk and it finds it (as long as it’s an Apple native app, or a third-party app that has been updated for iOS 9 compatibility). And if you want a shortcut to a commonly used contact or app, it’s right there on the new screen. 

Apple claims that the intelligence built into iOS 9 will learn your habits, and change the apps and contacts shown on the Suggestions screen to meet your needs. I can only guess that a week isn’t long enough to have trained the new system, or that my app usage is narrow and entirely predictable - either way, those apps have yet to change enough to suggest some magical predictive brain behind the scenes.

Elsewhere, you’ll notice that your beloved iPhone is subtly prettier - thanks to the new San Francisco font and some updated app icons - and a little easier to use. You can now switch back to a previous app, thanks to a new breadcrumb that appears at the top of the screen - no more closing and opening.

So for anyone upgrading their iPhone 5 or 6, they’ll get one new screen, a ton of smart refinements and one brand new app. But the real change to the iOS experience is reserved for buyers of the new iPhone 6s and 6s Plus.

You can’t accuse Apple of hype when it says that 3D Touch is an innovation that’s every bit as profound for touchscreen devices as the original tap, pinch and swipe. We’ve already had a quick hands on with 3D Touch on an iPhone 6s, and it will bring new, better ways of working with your content. And that’s not a claim that many mobile operating systems can make with a straight face, at least not in recent years.

Apple boasts that people are switching (back, probably) from Android to iOS, and has even launched an app to make the transition easier (which was duly trolled to within an inch of its life by the world’s Android fanboys). We can see why.

iOS may be a prison compared to Android - it’s impossible to customise the interface in any meaningful way, and the UI is stubbornly unwilling to bend with how you’re most likely to use your device every day - but it’s a brilliant form of incarceration.

Performance: enough to make you upgrade to a 6s

Apple hit a sweet spot with iOS 8.4.1. The latest update had ironed out just about every crease in iOS 8, to the point where our 64GB iPhone 6 Plus was about as near to perfect as any smartphone could be: two days' battery life in normal use, and an interface that was completely lag free. Heaven.

All of which makes the iOS 9 release something of a risk, made greater by Apple’s aggressive claims of improved performance and longer battery life (pride before the fall, and all that). But before we make a grand pronouncement on how successful Apple has been, we need to give a major health warning. The world’s app developers won’t update for iOS 9 compatibility for several weeks yet, so increasing the chance in the meantime of slowdowns, crashes and mysterious battery drain.

At least if the last week is anything to go by, the iOS 9 upgrade walks a fine line. On one hand, it’s snappy enough to make most iPhone 6 owners glad they made the upgrade (and the same can be said for the iPhone 5s, based on 15 minutes with an upgraded example). On the other, there’s a few slowdowns that may just be enough to nudge you into buying a 6s or 6s Plus.

In particular, the new multitasking screen is a slight disappointment on our 6 Plus. iOS 9 replaces the inefficient app-per-screen view of iOS 8 with a stacked deck of minimised app cards to horizontally swipe through (not dissimilar to the Android Lollipop multi-tasking view, but turned 90 degrees).

Of course, there’s every chance that yet-to-be-optimised third-party apps were slowing down the animation as we swiped through the new deck. But even when we closed all third-party apps and flicked through a deck of Apple's native apps, the slight jerkiness was still there.

There’s the same subtle slowdown when you pull down from a home screen to start a search - the transition looks like it’s running at a lower frame-rate than you expect from a leading mobile OS. Why do we get the feeling that it will be as smooth as butter on the A9-equipped 6s or 6s Plus? And why do we feel so cynical for thinking that the slowdown is deliberate? Perhaps it's because our immediate reaction when encountering the small lags was to start checking the price of a 64GB 6s Plus.

That said, the rest of iOS 9 is as smooth as it was in iOS 8.4: apps open and load quickly, and the swipe between home screens is instantaneous. And that’s a state of affairs that should only improve as app developers update for iOS 9.

Battery life appears just as good as with iOS 8, although it’s obviously too early to tell if it provides the improvement of up to an hour that Apple claims.

Our 6 Plus would end a normal day’s use at 65-70%, and a heavy day at 45-50%. A week with the 6 Plus running iOS 9 seems to be following the same pattern. Which, by any standard in the smartphone world, is bloody excellent. Avoid playing Riptide for five hours solid, or leaving every one of your installed apps to full sync and with notifications on, and you should get two days’ usage without even trying.

If the new 6s Plus has the stamina of its forebear, you’ll never need to use iOS 9's new Low Power Mode mode (although we’ll understand it coming as a boon to iPhone 6 owners, with its smaller battery).

Apple Notes: Evernote, it’s behind you...

There was a time - like, yesterday - when Apple’s Notes app had no excuses for its weaknesses. In the software development world, there’s a concept called Minimum Viable Product (MVP), in which you release the most basic version of your software to test public appetite for your idea, and then update it fast based on feedback.

Apple could try and claim that Notes was an MVP, but it would be a claim that anyone could shoot down in seconds. For one, it’s called a Minimum Viable Product - and Viable in the fiercely competitive world of note-taking apps means you need to be great straight out of the box. Notes has never been great.

Then, your MVP needs to update fast to keep pace with your users’ feedback. Yet Notes has steadfastly remained frozen in ice - the only real changes have been cosmetic, largely when Apple abandoned skeuomorphic design.

Until now, that is.

Notes in iOS 9 makes a serious leap in the direction of Evernote, the world’s most popular note-taking program. Before, it would only take text notes. Now, it will let you put pretty much anything into a Notes page, from a Word doc to a PDF to a bookmark clipped from Safari. And within the app, you can switch between typing and drawing in seconds, along with an admirable armoury of formatting options for text.

The upgrade takes Notes from almost forgotten also-ran to a serious contender. Especially given its instant sync through iCloud with the similarly upgraded Notes desktop app in El Capitan (due for release to OS X users on September 30).

Is it better than Evernote? No. Evernote is much more flexible - notes can be tagged, and there are reminders build right into the app (where Apple has a separate Reminders app, which, oddly, doesn’t seem to think that Notes exists - even though Notes now let you make checklists of… er, reminders).

But then Notes comes free with iOS 9. And if you don’t feel like splashing the cash on Evernote Premium for the year, Notes is now a credible alternative.

Apple Mail and Calendar: better… but third parties still hold the reins

The two staples of iOS both get upgrades for iOS 9. Mail can now handle attachments like a pro, and can detect missing contact addresses and events. And it goes without saying that the pair will be enabled for 3D Touch from Day One, and should be a delight to use.

Only… only, Mail still doesn’t support Push for GMail (thanks to a long-standing spat between Apple and Google), and an awful lot of people use GMail. Neither does it match the likes of Spark or Dispatch for clever tricks. 

Apple Calendar now does a much better job of creating events and inviting people - but with the likes of Fantastical and Sunrise on the market, it arguably had room to raise the bar higher. Don’t get us wrong: you’ll be happy using Mail and Calendar every day, and iOS 9 does much to further their causes. But better mail and calendar apps are a tap or two away, and many are completely free of charge.

Apple News: Flipboard, it’s behind you...

This, ladies and gentlemen, is Apple’s attempt to do for media what it did for music.

The new News app is an aggregator that replaces Newsstand, playing back feeds from a host of popular publishers and presenting the stories in a clean, simple interface that will be familiar to Apple Music subscribers (right down to the ‘For You’ tab).

If you’ve ever used Flipboard or Feedly, you’ll feel right at home in Apple News. Launch it for the first time, and you’re prompted to add channels and sources (which is as simple as tapping them). Pick a few sources, and you’re sent through to the For You landing page, which is where we guarantee that 90% of Apple News users will spend their time.

Functionality is fairly limited at this stage, but more than enough for most people’s daily news habits. You can scan a page of stories, open them, and save them for later. If you want to start tuning the content feed, you can add new topics - either run a keyword search and add the channel from the results, or tap a tag in a story that you find interesting.

Apple News isn’t constrained to the new app: the new iOS 9 Siri Suggestions search screen has News headlines built right into it, presumably an attempt by Apple to equal the contextual feed that Google has achieved with Now. But the integration ends there - there’s no Today screen widget, for example.

Security: go on, try - I dare you

When you first set up your upgraded iPhone, you’ll notice one small tweak that stands out a mile. Where once you had a four-digit PIN, you are now offered six digits.

Not the kind of thing that gets parties started, sure, but the extra two digits substantially reduce the chance of your device getting hacked. And it adds to a suite of security measures that are an appropriate response to the iPhone’s status as an emerging personal security nightmare (what else in your world has your credit cards, your friends' intimate details, the keys to your social accounts and - most terrifyingly of all - where you’ll be and when?).

Other measures in iOS 9 include a new interface for two-stage iCloud authentication, and introduction of the App Transport Security (ATS) standard for app developers, ensuring more secure connections when moving your data between apps and servers.

Siri gets serious

‘Hey Siri... what’s the weather like in Paris?’.

Imagine you’re Siri. Imagine the boredom. The same bastard question, again, and again, and again. But then, you did kind of bring it on yourself.

Most of us don’t actually have that many things we need to know by long-pressing a home button and asking the question aloud in public. And there aren’t that many places where having the answer read aloud is a social norm. So you shouldn’t be that offended that you’re still used primarily for (now-old) party tricks, or to test your knowledge of anatomical obscenities.

But that doesn’t mean that Siri itself is the wrong idea, or that its power shouldn’t be extended. With iOS 9, Apple’s blurring the lines between Siri and Spotlight search. The all-new Siri Suggestions screen is the 9‘s most extrovert addition to iOS, just a swipe to the left of the traditional iOS main home screen.

The new screen presents you with a search field, a panel of your most used contacts (which, Apple says, will adjust according to your iPhone usage), a panel of local services (taken from the updated Maps) and local news (taken from Apple News).

The Suggestions search field will take either text or voice inputs, and presents results in blocks according to the type of content (email, calendar, contact etc). Type a search, and it will run a deep search in your installed apps (once they've been updated for iOS 9 by the developers). This feature was added to Android some months ago, and in theory should be dream - sports results from ESPN, restaurants from Yelp etc.

Problem is, we’ve rarely used it on Android, and we're sure that it will be a regular destination in iOS. More useful, perhaps, is quick searches for mail and calendar events, both of which the new Siri Suggestions performs admirably quickly. And we’ve already found myself swiping left to call friends and colleagues, rather than opening the phone app.

Suggestions isn’t the only Siri upgrade in iOS 9 though. Siri can now be set to be always on (although only when your iPhone or iPad is plugged in, presumably a result of the extra power drain that’s a consequence of having it in permanent standby), and there’s a new voice-recognition trainer to promote the always-on feature when you first install iOS 9.

When was a new font ever exciting? Try now.

Jony Ive knew that Helvetica Neue was wrong when he chose it as the default iOS 8 default font. Or if he didn’t, he should have done.

In some sizes, Neue is about as close to perfect as a font can be. But in too many places on a smartphone, where it was forced into smaller sizes and trickier spaces, it was both inefficient (it’s relatively square, and therefore wide) and not particularly pretty.

Apple introduced the San Francisco font when it launched the Apple Watch. The much smaller Watch screen demanded a more space-efficient font, which meant something narrower. It also meant concentrating really hard on readability at much smaller text sizes. So when it came to developing iOS 9, the San Francisco font was ready and waiting.

And the great news is that it works beautifully. In fact, the entire Apple software suite is clicking into place - El Capitan is the fully realised version of a visual journey that began two years ago, and much the same can be said for iOS 9. If you like staring at interfaces, these are the places to stare.

iOS 9 verdict... for now

iOS 9 is either brilliant, great, or frustrating. Which of those three experiences you get will depend on your luck, and your hardware.

We’ve read enough forum posts complaining of post-iOS 9 slowdowns to know that the upgrade doesn’t play nicely every time; if you’re one of the frustrated unlucky ones, our sympathies. All we can suggest is that you clean re-install from Recovery, or reset without restoring your old data. 

However, for the majority of people, the new OS is great. It joins a whole lot of dots that needed joining in the iOS interface, improves your device’s security, and makes your content easier to find. What’s not to like?

Better still, if you’re buying a 6s or 6s Plus, 3D Touch will - we safely predict, and hope - change how you interact with your smartphone forever, and we somehow suspect that you’ll see none of the slight slowdowns we’ve experienced on our first-generation 6 Plus. 

We'll update this review once we've spent a bit more time with the new OS on the new devices but even before then we're happy to pronounce iOS 9 a success. 

Stuff says... 

Apple iOS 9 review

Apple's latest mobile OS is its smartest and slickest ever - so long as you're using the right phone
Good Stuff 
Superb search functions
Improved Notes, Mail, Calendar...
Improved design and font
Bad Stuff 
Jerky performance on some older phones

Where to buy Apple iOS 9: