Peter Parker transforms from Spider-Man to Lounge Lizard in “Spider-Man 3.” It’s a dippy mash-up/wrap-up of the Spidey franchise that turns nerdy little Parker – played by nerdy Tobey Maguire – into a “playa,” complete with Armani suit and Travolta-“Saturday Night Fever” walk.

Didn’t see that coming, did we?

Not any more than we anticipate the whole loony middle act of “Spider 3,” in which the best of the comic-book movie series is reduced to outtakes from Jim Carrey’s “The Mask.” It’s crowd-pleasing goof, this Spider-Man-as-dancing-jazzman bit, but at the cost of a coherent, smart movie.

Sure, “Spider-Man 3” has more supervillains and more dust-ups with them. Literally.

Because this time, the heavy heavy is The Sandman, the molecularly-altered career crook played, when he’s at his most human, by Thomas Haden Church. He emotes and gives us bad-guy motivation (his daughter is trapped in HMO purgatory) and kicks up a sandstorm whenever Spidey crosses him. It’s a nice effect, and was way back when it first turned up in “The Mummy” movies.

Meanwhile, “Your friendly neighborhood you-know-what” has crossed over into the Dark Side. Also literally.

A meteor plops near a spot where Peter and Mary Jane almost make out, gloms onto Peter, and makes him and his suit all dark and dangerous.

Thus, the Travolta walk.

This alien spider-blob is just accentuating Peter’s personality flaws. His ego was already a bit out of control. He says “They really love me” more than Sally Field as he basks in the big city’s “NY Hearts Spidey” glow.

He’s so full of himself that he can’t see MJ’s Broadway debut for the clunker it is (Kirsten Dunst bravely sings, badly, for the role). He only sees the positives when he gives his nemesis, Harry Osborn (James Franco), a bonk on the head and makes him lose his memory of hating Peter.

Peter sees a threat to his Daily Bugle gig. A new photographer (Topher Grace, in curls) is the guy willing to cross any line to get the photo. But Peter doesn’t see the threat that a newly nice and still-rich Harry could be to his romance with MJ.

It’s funny to see Franco lift his game to play variations of Harry’s personality, and Dunst has never seemed more Plain-Jane vulnerable nor too-good-for-the-material than she does here. But Maguire’s performance leans toward perfunctory.

Director Sam Raimi gives his brother Ivan a writing credit on this cut-and-paste job. He still has actor-brother Ted in the story as a newspaper marketing moron who draws the ire of ever-fuming editor J. Jonah Jameson (J.K. Simmons).

Raimi has made a pandering movie with flags and firefighters in many a scene, almost daring us to dislike this $300 million-plus money machine. The brawls have a repetitive familiarity to them, as does the big theme of the film: forgiveness.

Raimi does manage one smart indulgence. His screen alter-ego, Bruce Campbell (“The Evil Dead” films), steals a scene as an oh-so-zilly, oh-so-French maître d’.

It’s great that these movies give villains heart and soul and motivation. But Raimi’s everything-including-the-kitchen-sink third film robs the Spider-Man movie myth of its lightness. He has taken something heartfelt and witty and reduced it into just another comic-book movie.