Spider-Man has had a number of hit-and-misses when it comes to animated versions of himself. Either he's done quite well, or quite poorly. Spectacular Spider-Man, however, is the webslinger's best animated work by far, for a number of reasons.
The first, by far, is the script. It's taut, witty, and places extremely close to the comic mythos. Spider-Man's quips come across as genuinely funny, while the teenage angst sets the tone for Peter Parker's awkward life. It never feels corny, nor too serious; it's a perfect blend of fun.
Second, also by far, is the animation. Spider-Man's movements are fluid and fast, as are the movements of his enemies. Fights go all over the place, and can be quite over-the-top, but you never feel things are getting ridiculous. You really feel like Spider-Man is fighting tooth-and-nail when he tangles with foes like Doctor Octopus, Tombstone, Green Goblin, or Venom.
Third is a well-done all-star cast. This show uses many staple characters from the Spider-Man comics, and portrays them very faithfully (at least, from what I've heard). Nods to the comics are everywhere, and while a liberty or two may be taken with a character, it never feels like a disservice to the originals.
Spectacular Spider-Man is easily the best Spider-Man cartoon to date, and may well be the best Marvel Comics cartoon to date as well.
I patiently await (and hope for) the third season's arrival.