The positional defending system from PES 2011 which, to be fair, has been largely copied by FIFA 12, feels a bit less stiff and robotic. There's a new collision system, too, which reacts specifically to the area of impact triggering unique animations. It's impressive, but less fluid than FIFA 12's new physics-generated Impact Engine.
Best of all, players no longer get 'locked' in collision animations, so you retain control and can still offload the ball, even as your player locks shoulders or stumbles.
Another key change is that the CPU AI applies a lot less mindless pressure, which is to say that the game plays more like a human than a robot, allowing you a bit more time to pick a pass. This works in tandem with the noticeably enhanced new off-the-ball AI, where teammates make dummy runs and overlaps to buy space.
It's a big improvement over the frustratingly stiff PES 2011, where you'd find yourself shouting at the AI to make runs, but the lack of a 'run prompt' button, like FIFA, is still frustrating.