Of course there are a lot, but the most recent game that made my jaw drop at every turn and made me think "this is how gaming SHOULD ALWAYS be" was
Those dungeons were so well designed... yes, I was always aware I was playing a game, but ever realising how great this game was. And this is no nostalgic memory, mind you: I played the game for the first time half a year ago! Not only is it great, it stands the test of time superbly ^_^ Brilliant design simply never fades.
