I liked it. Considering the censors and animation difficulties they had to work around, I think it was great. The characterization was spot-on for almost everybody. Spidey's quips were funny, particularly. And you gotta love how the show introduced kids to Marvel Comics.
I liked how each season had at least one story arc (although the Morbius story ran a little long). It featured what's probably the best version of the Alien Costume Saga ever (and it introduced the concept of the suit amplifying the wearer's negative traits, a concept used in every subsequent iteration), as well as the only appearance of Carnage in animation (Dormammu aside, it was still a very well-done portrayal).
Oh, and don't forget the guest stars. The Punisher, Daredevil, the X-Men, and Doctor Strange!
The quality of animation was unforgivable, though. The censorship was ridiclous at times, too. I mean, the police had lasers? No one could throw a punch or say "die"?
Also not a big fan of some of the character designs (Peter Parker's not supposed to look like a bodybuilder. Dormammu wasn't all that scary-looking. And what was up with Venom's lips?) Although some were nice (MJ in those jeans and boots...)