Lumbering into theaters this week to establish box office dominance for – well, at least until “Shrek the Third” comes out – “Spider-Man 3” is more sprawling and ambitious than the previous three installments, taking a deeper look (for a comic book movie anyway) at the evolving relationship of Peter Parker (Tobey Maguire) and Mary Jane Watson (Kirsten Dunst) and exploring a darker side of our formerly squeaky clean hero.

At the outset, Peter has finally achieved something of a balance between his “normal” life and his costumed antics. MJ is starring in a Broadway musical, he’s doing well at school, and the fickle citizenry of New York are finally coming to appreciate that weirdo in tights who sticks to walls.

Because this is The Movies, such an idyllic state can’t last. Sure enough, Peter’s life is complicated by the arrival of Flint Marko (Thomas Haden Church), a prison escapee caught in an experiment gone awry that transforms him into the Sandman (you’d think something called a “particle physics testing facility” would have stouter defenses than a mere chain link fence). And in a stunning plot contrivance twist, it turns out Marko is the guy who actually killed Peter’s Uncle Ben (continuity be damned). Upon learning this, Peter will stop at nothing to capture him. Trouble is, the Sandman is one tough hombre, and isn’t as easily brought down as, say, the Ringer. Just when it seems all hope is lost, he acquires a new black suit, courtesy of an alien symbiote that conveniently falls to earth in a meteor that no one else in the city sees.

Lucky break, right? Well, yes and no, because while the new and improved suit enhances his abilities, it also brings out a darker side of Peter’s personality. He starts behaving distinctly…un-Spider-Manly, scamming on the ladies – including lab partner Gwen Stacy (Bryce Dallas Howard) – and blowing off Mary Jane. Luckily for her, Harry Osborne (James Franco) is still around, and only too willing to comfort the lady fair ever since his pre-emptive attack on Spider-Man (as the “New Goblin”) resulted in extensive memory loss.

The good news, to fans of the franchise that is, is that “Spider-Man 3” is more of what they’ve come to love. Your friendly neighborhood wall-crawler does battle with a slew of villains, and these sequences are the most visually impressive we’ve seen yet in the series. Director Sam Raimi’s trademark style is still here, and yes, there is a Bruce Campbell cameo.

The bad news is that the third installment is overlong, crammed full with a repetitive romantic plot, and just plain excessive. Raimi appears to be suffering from Peter Jackson syndrome, in that every idea he comes up with simply has to make it on screen. Was the entire montage of “Evil Peter” sauntering down the street and doing a goofy and incongruous dance-off in a jazz bar not enough to convince us of his slide into the dark side? As if the bad emo haircut and eyeliner weren’t enough, that is. One can almost hear the cops: “Don’t shoot, fellas: it’s the bass player from Fall Out Boy!”

There’s a climactic battle (Sandman is joined by fan favorite Venom, eagerly portrayed by Topher Grace), frenetic Raimi-style battle scenes, a death or two, and about three endings, each one going on longer than the last. It’s pretty to look at, and easy to follow, but nobody’s buying tickets to see MJ bitch at Peter about not understanding her feelings. The whole argument could’ve ended with Peter asking MJ how many children she’d saved in the last month ‘cause I bet Spider-Man saved about 30.

“Spider-Man 3” is rumored to be the last in the series, or at least the last one with the current cast and director. If so, it’s a fitting end to the trilogy, with the larger plot threads tied up but a few directions available for exploration, should the studio approve.

And considering the movie’s probably going to gross $750 million worldwide, I see no reason why they shouldn’t.