I downloaded the FIFA demo, and I must say I wasn't impressed. While the players do move very realistacally, which is nice to watch, it makes for poor gameplay in my opinion. The players still run like they are playing on 6ft of treacle.
Also, I don't like the shoting at all, it doesn't feel powerfull enough. The referees as well, blimey, they are shocking. People talk about how bad the PES refs are, but FIFA is on a par with PES5 for bad refs. Playing against my mate, he tackles me front on with A, takes the ball clean as you like, and I win a penalty. I was baffled, frankly.
Graphically, hit and miss. The players do look superb, and I would like to see it in HD, but some things were crap. The pitch, for example, looks laminated in areas, or like Mr Sheen has spunked everywhere or something. Very shiny.
It obviously has more features, but the gameplay, the real issue, is still inferior. If I were to buy either, it would be PES, despite the fact I already own the even-more-superior-to-FIFA PS2 version.
So there.