MLB 2K12 graphics: Man, those graphics are AWFUL.
NBA 2K12 graphics: Yeah, the gameplay is AMAZING! Graphics aren't even that important, as long as the gameplay is solid, etc.
My point? 2K has never had overpowering, or even truthfully good looking graphics. They've always been a step above the last-gen graphics, basically.
I will say this though: Don't know if this was in 2K11 since I didn't play it last year outside of the demo, but I did notice some "emotion" in the players (Verlander did a little snarl/gritted his teeth as he threw the pitch; batter throwing down his bat in disgust). I think emotion is always a good thing in sports game.
I will have to try the demo out to determine whether it's worth buying, and even that may be a wait since I'll most likely be grabbing Resident Evil and Final Fantasy