Well, nobody got or even attempted #6, so:
6) Portal 2
The original Portal was a breath of fresh air, but it was short and never really got very deep. Portal 2 was better in every concievable way. GLaDOS had even more great lines than before, and she was joined by two excellent characters in the form of Cave Johnson and Wheatley. The campaign was significantly longer, introduced a range of new gameplay mechanics and created puzzles that actually became difficult towards the end. There was a proper storyline with changes of setting. The co-op gameplay was nothing short of outstanding. There is almost literally nothing to dislike about this game, and yet it wasn't even my favourite game of 2011.
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