I just downloaded the demo, so I believe a bumpage is in order.
You get to play a 6 minute half of Arsenal v AC Milan at Highbury, followed by a penalty shoot out if scores are even. I've found what's different with 2004
a - Reyes plays for Arsenal
b - The throws are done much better, and you can make breaks from the defender as the player is about to throw the ball
c - I find it harder to get booked
d - Off-the-ball seems to be done better. I still can't use it though
e - The one-touch passing (using X on the PS2) seems to be done better. It seems that the players are more intelligent and will look not to play it straight at the man, but they'll make runs/dodge defenders etc. to get the pass to its target better.
f - They seem to have taken away the 'lunge' (using O on the PS2).
g - Goal celebrations are better