As Spider-Man 3 opens with shards of glass that depict highlights from the two preceding and outstanding Spider-Man films, the symbolism suggests that our hero, Peter Parker (Tobey Maguire), will once again seek to understand his identity—shattered and broken by the challenges he faces in the latest film.

Everyone’s favorite nerd-turned-superhero broke first day and opening weekend box-office records, snatching $148 million in its first three days and $59 million alone on Friday, May 4. In a franchise like this, each film builds on the success of its predecessors. Unfortunately, Spider-Man 3 fails to do much more than rest on their laurels. The 2-hour and 20-minute story drags, its multiple subplots are overkill, and the string of hit films that leaves fans wanting more is broken.

Most disappointingly, the much-touted prospect of watching Spidey wrestle with his dark side comes off as contrived, although it could have been much better.

In the first Spider-Man film, Peter Parker was bitten by a radioactive spider and found, in his new identity as a superhero, that with great power comes great responsibility. In Spider-Man 2, Peter discovered that heroes sometimes must sacrifice even their most deeply desired dreams to fulfill their calling. In Spider-Man 3, he wrestles with the dark side of his identity.

“Who are you?” asks Mary Jane (Kirsten Dunst). “I don’t know,” says Peter, who begins to fall in love with his public persona, to ignore others’ needs, and to lose his identity as a caring, self-sacrificing person.

A cinematic exploration of the lure of fame and the affects of adulation would have made a great Spider-Man film. Based on the strength of the first two films, that’s what many Spider-Man fans expected out of the third film in the Marvel Comics franchise. But instead, Peter’s misbehavior—sometimes bordering on the absurd—is explained away by the impact of a mysterious black goo that emerges from a meteorite that just happens to strike Earth a few feet away from where Peter and Mary Jane enjoy a quiet night gazing at the stars (and oddly not seeing the meteorite land).

The black goo turns out to be a symbiote—a parasitic living alien organism—that makes Peter more aggressive and brings out his dark side. So it’s not really Peter who humiliates a rival photographer Eddie Brock (Topher Grace), disfigures his best friend Harry Osborn (James Franco), and seeks revenge on escaped thief Flint Marko (Thomas Haden Church), who was responsible for the death of his Uncle Ben. Good Peter Parker didn’t do these things. The goo made him do it.

Spider-Man’s rivals have their own justifications for the choices they make. When the goo attaches to him, Eddie becomes Venom, a negative mirror image of Spider-Man. Harry long before had chosen to follow in his father’s footsteps as a second Green Goblin. Marko, while fleeing police, finds his way into a nuclear particle test facility, where he is inadvertently transformed into the Sandman—a villain who can take shape as a gigantic sandstone pillar or a wispy sandstorm.

While Spider-Man 3 explores the motivations behind the villains’ choices, it would have been a stronger film if Peter had truly wrestled with the dark side of his own nature—rather than a false one created by intergalactic goo. Certainly the murder of a beloved family member is sufficient justification on its own for anyone to desire to seek revenge.

Instead, Peter’s behavior and the color of his Spider-Man suit are transformed by what seems to be a cheap and far-fetched plot device. It’s all easily explained away so it’s not really his fault. In such a polite age as ours, it almost begs the question of whether we believe that it’s possible for a genuinely likable person to have a dark side. I’m OK, you’re OK—but watch out for the goo from outer space.

What a stark contrast to these words spoken two centuries ago: It’s not what goes in that defiles a person, but what comes out.

Spider-Man 3 ends up as a gooey mess and a disappointment—even though it very likely will continue its box office success on the strength of its previous films. Cynics would suggest that the Hollywood always prefers good marketing over a good story. But perhaps Director Sam Raimi and his writing collaborators—his brother Ivan Raimi and two-time Oscar-winning screenwriter Alan Sargent (Julia, Ordinary People)—have some other excuse.

The goo made them do it.