At the moment, going off those E3 build videos, the only noticeable differences between 2011 and 2012 are in the gameplay itself. The presentation, menu flow, intro-sequences, graphics etc. seem to be almost identical to PES2011. I'm hoping that some of this stuff is placeholder, and that some of the final assets have yet to be implemented.
It's been said by Konami that the real improvements this year are on the pitch, and that does appear to be the case from what i've seen so far. The game does appear to flow much better, and that strange disjointed feeling that was present in 2011 seems to have been eliminated. The ball physics look better at this stage, as do some of the animations. Obviously, there were some that were in 2011, but I also spotted some new ones in there that looked fairly decent. I'm glad that the old wide cam has made a return as well. That new camera just didn't do it for me; I found it tricky to judge the trajectory of the ball.
No one is going to know just how good PES2012 really is until a good couple of weeks after release. The thing that annoyed me most about PES2011 was that for every good game I had, the following game would be dreadful. There were far too many "what the fuck?!" moments to make it a truly enjoyable experience. This was something that I had begun to notice after around 10 days with the game, so the same time will be needed to fully evaluate 2012. I must say though, the videos do show some promise.
There's a definite divide between the different PES community forums at the moment. It's all dizzying optimism over at WENB, whilst here at Pesgaming there seems to be a lot more cynicism and pessimism towards PES2012. I think there's definitely a case for both of those given what's happened in recent years, but i'd say i'm somewhere in-between; cautiously optimistic. I definitely want PES to reach the heights it did all those years ago with PES3-6, but I do wonder if Konami will ever be able to pull it off. I guess we'll have to wait until the demo to find out!