From the video's i've seen they've made massive changes to the AI, players always looking to make runs when you're on the ball, defenders actually working as a proper unit instead of just running around hap hazard, massive improvement on last years in my opinion.
FIFA just doesn't do it for me, last years game went really really slow, like they were trying to force you to play possession football, the players all seemed clunky and immobile making dribbling feel heavy and unresponsive, then you have the classic FIFA problem, you're rarely able to beat a man without using the right stick to do some sort of knock or trick, a change of pace or direction is rarely able to do the job on FIFA.
Ever since i was introduced to PES i've always thought it was the better footballing game, it feels so much more natural to me, but it always lacks polish so you have to put up with some annoyances to enjoy it, this years problems being poor keepers and AI. I wish someone would throw a massive amount of money at PES to bring the other areas of the game upto the standard of FIFA because i think the basics of the football have always been superior.