Sandman and Venom and Harry Osborn and the alien costume and Peter Parker himself are all villains in this one, and it’s just too damn much. The great superhero movie rewatch slogs through the overplotted mess that is Spider-Man 3.
The best superhero movies are ones that distill decades of comics stories into a single film. The worst are the ones that try to compress decades of comics stories into a single film. Spider-Man 3 is one of the latter. As seen above, Venom’s backstory was complicated enough, and they try to shove it all in there, from the alien’s history as Spider-Man’s new costume to his getting rid of it to it taking over Brock, plus also giving Brock a proper setup instead of shoehorning him in the way David Michelinie and Todd McFarlane did in 1988. On top of that, Harry’s arc covers a ton of territory (which took the better part of two decades in the comics), from his learning his father was the Green Goblin to getting amnesia and forgetting to remembering again to taking up the mantle of the Goblin to redeeming himself in the end and sacrificing his life. Plus there’s MJ and Peter’s relationship drama and adding the Stacys to the mix.
Oh, and then there’s the Sandman. Hilariously, given that it was the original base of the film, the Sandman is utterly superfluous to it. If you excise the Sandman from the movie, it changes very little except for the climactic fight, in which Sandman is a boring CGI monster. And honestly, Venom has always been a tough enough foe that they could have kept it to just him and still challenged the combined might of Spidey and the Goblin.