Funny you should mention Planescape, actually, as i've recently been playing Alpha Protocol- which borrows quite a few elements from it. The adaptation of the story is the best i've seen in any game to date- MUCH better than that in Deus Ex (Which doesn't actually give you that many choices with regards to the story, so I don't know why people regard it so highly). Plus the game is just genuinely fun, which is all I want.
Above that, though, i'd probably say DJ Hero. Genuinely one of the best experiences i've had in gaming in the last few years- the setlist was perfect, the difficulty was just right- and with the release of the Domination Track pack, I can officially claim to be in the top 25 for something (Not counting all those RB1 vocals which I seemed to be the only one playing).