That's the thing--Spider-Man 2 was rather flawed overall. The main story missions were meh, and the side missions got tedious after awhile (how many people in this damn city are hanging from a ledge at any given moment?). It was much like GTA3, where it was almost a chore to make myself finish the thing, and I'd normally just fire it up to swing around town aimlessly. I'd probably only rate it an 8/10 overall (at the time). It just had the advantage of absolutely
nailing the feeling of web-slinging in a way that no game ever did or arguably did again until Spider-Man (2018).
USM was definitely a downgrade on the freedom/webslinging front, but pretty much everything else was better, and it was a tighter experience. I guess it comes down to whether you're the type who prefers the game with the better overall package, or the game with one killer feature that it does really well and you can't find anywhere else.