USM had better fluidity in the movement, adding the horizontal wall runs, and mid air double jumps to keep your momentum.
Sadly, they slowed the speed of the swinging down so much from SM 2 that it really wasn't that thrilling to websling like it was in SM 2. And that one button combat system was just pure ass. Pinball Spidey was not fun at all.
Plus, making Venom just a bad Hulk Jump ripoff for his main mode of travel was crap. He should've been able to websling like 616 Venom.