Don't own Fifa 10, but have played it regularly at a friends. I thought the demo was brilliant, noticeably better than 10 in the following areas:
-Tackling
-Fouls
-Dribbling
-Presentation
-Overall smoothness of the animations
Still have yet to determine if its a purchase for me. Seeing as I didn't buy Fifa 10, I'll probably shell out the dough for this.