Another few to add to my list:
Mirror's Edge - I wasn't sure about this after hearing mediocre reviews, but man it's awesome, imo it's one of them games where you really shouldn't listen to reviews.
ArmA Armed Assault + Queen's Gambit - It took me a while to get into ArmA, but I found it to be very immersive once I had. Just a shame it's so unstable, it uses more resources than any other game I've played. But what's with the fugly reload anims and incredibly annoying engine sounds?
Portal - Need I say more? Except that the cake is, of course, a lie.