I actually liked most of Spider-Man 3, but I agree that they packed way, way, way too much in (there was a plan to make 3 and 4 back-to-back, though that usually happens with mixed results in these sorts of things...). And a lot of things ended up bugging me about it:
-The music: Christopher Young was a poor choice for composing the score, especially when he's following up Danny Elfman! His music choices were, if not bland, then outright absurdly over-the-top, like Harry's death scene. If they didn't do the whole "build to a sentimental crescendo" with the sun rising in the background, that scene would have been a lot better.
-Which brings me to the dialogue: while not as bad as the first movie, the dialogue was still very bad. The entire plot of the movie hits all the right beats, but it's undercut by how sappy it gets (the butler telling Harry the truth about Norman, and about how his friends love him, and la de da de da). Like with the sentimental music, this just makes what should have been great scenes seem like a Hallmark TV movie.
-And speaking of the wrong tone: I actually wouldn't have minded the dorky-evil Peter Parker, or his dancing, IF it didn't come after his attempted murder of Sandman, and his vicious battle with Harry. It seemed like that scene, though in a milder form, should have been earlier in the movie. The idea Sam Raimi had of showing that going "dark" or "bad" isn't cool wasn't a bad idea, but they needed to start out with Peter just being more cocky, though being completely foolish as a result, and building to "Holy shit, he's trying to kill people! He's gone nuts!" Once they established that he had gone to viciousness, not only did they take a step back, it also eliminated any drama they were naturally building towards by doing the dancing segments, so it was unnecessary, sort of like...
-The crowd in the climactic fight scene. Ugh. Turning a gut-wrenching blood feud into a spectator sport for New Yorkers to gawk at slack-jawed? Once again, they eliminated the impact by cutting to unneeded newscasters and children going "Wicked cool!" to sell the scene rather than the images selling the scene. That fight only got good when it went away from the "ooh-ahing" crowd, and then it was only for a few minutes.
-Oh, and Mary-Jane being in danger, yet again. Granted, it probably wouldn't have made sense to have someone else in danger if the goal was to get Harry to become a good guy, but in that case, why even have the damsel-in-distress plotline? By that point, I was hoping they were past going to the tired plot devices like that (since they clearly were going for something different), but then Venom nabs her and it's "Here we go again."
The ultimate feeling I get from the movie is not that it's bad, just that it was sloppy in that trying-too-hard-to-do-everything way that's just really irksome. There was nothing wrong in the script that a little judicious editing couldn't handle. Add in a different composer (Clint Mansell, maybe? Howard Shore? Marco Belltrami? Reconcile with Danny Elfman?), and the result would have been, if not the best of the three films, then certainly a contender.
