1. Portal (2007)
They only went and brought some sort of new idea to the table. Portal initially looked like it was going to be about shooting men or aliens in grey corridors, but really it was a 3D puzzle game in which you warped around, trying to escape its many chambers, at the behest of a weird robot lady voice. We shouldn't really have been suprised by how good it was, given that it was made by Valve - the masterminds behind Half-Life and Steam - but puzzle games are never usually so... exciting. It was also graphically slick, with bags of humour and charm. But its real genius was in how brain-shatteringly clever it was. To properly understand some of the puzzles, you'd need to be a mathematician specialising in non-Euclidean geometry, but that didn't matter, as trying, trying and trying again to solve them was never anything less than tremendous fun. Portal 2 wasn't bad either.