7. R-Type (1997)
One of the most ported, converted and pirated games of all time, and for good reason. It was, and still is, a highlight of the 2D space shooter genre, combining clever levels with weird weapons, a great graphic style and memorable tunes.
More after the break...
6. Counter-Strike (1999)
Built on the engine that was already familiar to Half-Life's vast legions of players, Counter-Strike introduced a concept that still dominates gaming today - teamwork. If you don't know where your teammates are and work with them to provide cover, you have a life expectancy on a par with a depressed lemming on a clifftop holding a bag of explosives and a lit firework. And when you do die, which you inevtiably do (as a favourite of pro gamers, Counter-Strike is a crossfire hurricane of well-aimed bullets), you have to wait out the round.
5. Gears of War (2006)
As if the Halo series wasn't dumb enough, Microsoft and developer Epic then created this. It's basically a Vin Diesel simulator, in which comically shallow characters swear and bluster through teenage sci-fi cliches. Your gun has a chainsaw stuck to the front. Needless to say, it is absolutely gigantic fun.