Undoubtedly Mass Effect 2, and closely followed by Borderlands (still haven't completed the latest DLC, and have yet to start a new game with two of the four available characters, it's quite a big game). I still haven't touched BC2's single-player, I went directly with its multi-player component... I'll have to find the time to do all of that and more with my games, I've been more busy than usual with my job since the past two months or so.
But, yes, to repeat myself, of the "latest" shooters ME2 is definitely the best, in my opinion.