It is nigh unto objectively true that Spider-Man 3 is not nearly as good as its two predecessors, but that is not quite mean that it is in fact bad. It's a good comic book movie that suffers only because everyone expected (reasonably) that it was going to be a masterpiece.
There are, I think, two separate but parallel flaws. The first is one of tone: this by far the darkest story that Sam Raimi and company have essayed in the three films, concerning Peter Parker's growing obsession with his own legend, literalised in his encounter with an alien symbiote that turns him into a swaggering and violent show-off, emotionally and ultimately physically abusive to those close to him. On paper, this is a perfectly reasonable extension of the concerns covered in the first two films: in each film, Peter is a bit more of an adult, and in each film he has a harder time clinging to the idealism that drove him. It was easy to be a superhero adolescent, but being a superhero adult is something of a bitch.
It's not at all clear, unfortunately, that Raimi is anxious to follow his hero. His sensibilities in the previous films was very 1960s, befitting the character's origins; and the director brought a sense of playfulness to the goings-on that kept the films light and exciting even as they followed some very precarious psychological turns. There's not an obvious shift in directorial emphasis in the new film, but somehow it feels more campy; perhaps because the drama is more dramatic, the comic bits seem more out of place. And the dramatic bits, in turn, feel flat and tossed-off.
The second flaw is Tobey Maguire. Like Raimi, I think that he has not perhaps grown-up with the character. Indeed, this was my chief complaint about Spider-Man 2, and (notwithstanding my propensity to joke about replacing my beloved Willem Dafoe with Alfred Molina) the primary reason that I think the second film didn't quite work as well as the first. Maguire seems too attached to the character's gee-whiz naïvete; although who truly can know what goes on inside the head of an movie star? I cannot explain why Maguire does what he does, I can only argue that what was a distraction in the second film turns into an outright liability here, where we're supposed to believe in Peter's edge and new found assholitude. Instead, he feels like an overgrown kid playing at being a grown-up jerk. It's funny at times - particularly when the symbiote-afflicted Peter walks down the streets doing that finger gun thing at every female he passes by - but the mere fact that it's funny means it's rather aggressively at odds with a mostly violent and bleak storyline.
Despite all of this, I enjoyed my time well enough, certainly more than I recall enjoying any of last year's big movies. Let us not forget, the last twelve months have borne witness to X-Men: The Last Stand, Superman Returns and Ghost Rider, a trio of films that were respectively dull, mirthless and insulting. Spider-Man 3 doesn't, perhaps have such a high bar to clear, but it clears it. There are two perfectly fine action setpieces (the sequence that occurs near the beginning of the film is possibly the best-looking and most exciting bit in the whole trilogy). Moreover, while the film is dangerously silly, it's silly in a very recognizably Sam Raimi sort of way; and while that does not mean "this is a great superhero movie," it shouldn't necessarily impugn any of the fun that's to be had. Raimi's films are possessed of a very particular kind of gonzo energy that is appealing all on its own. For starters, Bruce Campbell naturally cameos yet again, and its his best role in the series thus far, given the standards to which we hold Bruce Campbell roles.
I also had a whole lot of fun - and this is where I will part ways with just about every sensible critic in North America - with the forthright absurdity present in the film's three musical numbers, and yes you did read that correctly: the film more or less opens with Mary Jane (Kirsten Dunst) performing a '40s-style Broadway number, and there are two dance scenes set in a kitchen and in a jazz club, respectively. None of these (particularly the latter dance number) add anything of remote narrative value to this 140 minute beast, yet they are without question my favorite parts, the parts where Raimi seemed to communicate directly with me. Not because they speak to any sort of attachment I have to the material, but because I really want to think that if I were handed $250 million dollars to make a superhero movie, I'd make damn sure it had a few '40s-style musical numbers. You know, just for the hell of it.
Back in the real world, it's worth noting that most of the cast outside Maguire does a pretty fine job: Dunst still doesn't have much to do, but new villains Sandman (Thomas Haden Church) and Eddie Brock/Venom (Topher Grace) are well-played even if they are not brilliantly written, nor do either of them have remotely enough screen time to register as characters, nor do you ever forget that Raimi didn't want to include Venom at all until Sony pushed the character on him.
So yeah, the film drops the ball on characters, and the plot is a bit thin, but history is littered with middling-to-awful third films.* Spider-Man 3 is neither middling nor awful. It's disappointing, but still better than any major summer release since Batman Begins in June 2005. It ends the trilogy not with a bang but neither with a whimper (and rumours of Spider-Man 4 notwithstanding, this is a pretty clear closure-granting type of story). I liked it. I wanted to love it.
I must, however, confess that I am not just disappointed but actively pissed that the film was shot in a 2.35:1 aspect ratio (après no. 2, because of Doc Ock) and not in a 1.85:1 ratio (après no. 1). I'm not joking, either - it really annoyed me throughout the film. I'm no huge fan of 'scope, and I like it when major tentpole releases have the balls to go narrow. This is not the sort of thing that normal critics or viewers give one half of a tinker's damn about, but that is the effervescent magic that is me.