#33 Portal 2 played on PS3 and PC, released 2011
Portal 2 improved on it's predecessor in pretty much every way but the original novelty factor. It has a bigger campaign with some interesting glimpses into the back story of the facility. Great humor, a great new character and excellent new mechanics for the puzzles. The voice acting was top notch and the added commentary notes made a second playthrough all that much more enjoyable.
Still it would have been nice to see some more information on what's been going on outside or a glimpse in the lives of the people that worked there. The facility and offices you find are quite sterile apart from the science project room.
I have yet to play the co-op but I hear it's fun too. My wife and I tried to play it but it just showed again how unnatural first person dual analog control is for someone who's not used to it.
A great game overall, which I will fondly replay in years to come.