13. Portal 2 (PC, also on 360 & PS3)
What to say about a work of pure genius? The original Portal was fun. Short, unpretentious and pure gaming fun. Portal 2 could have just continued with the same, but instead added some fantastic new ideas, more mind-bending puzzles with some hilarious characters and great humour. The story mode alone really was comedy value and could have justified the asking price alone. Steve Merchant was great and really helped set the tone at the start of the game with comments like
"Most test subjects do experience some, uh, cognitive deterioration after a few months in suspension. Now, you've been under for quite a lot longer, and its *not* out of the question that you might have a *very* minor case of serious brain damage! But, don't be alarmed, alright? Uh, although if you do feel alarmed, try to hold on to that feeling because that is the proper reaction to being told that you've got brain damage."
The added co-op mode though really added to the value, although I have yet to complete it. What I have played though has been pure gaming bliss.