It's not exactly ripe material for satire: Ben Stiller's been kicking around the idea for Tropic Thunder since the late '80s, when actors in Vietnam flicks like Platoon and Hamburger Hill prepared for their parts by going to fake boot camps. The movie also mines inspiration from the absurdities of Hearts of Darkness, the documentary about the filming of 1979's Apocalypse Now, in which Francis Ford Coppola's movie about the horrors of Vietnam takes on its own Vietnam-like horrors.

Are you laughing yet? 'Cause Tropic Thunder's a comedy!

Stiller plays Tugg Speedman, a depressed, lonely action star whose best years are well behind him, and who dreams of saving pandas and adopting babies. Meanwhile, Jack Black is Jeff Portnoy, a maniacal drug addict/actor who's best known for movies like The Fatties Fart 2, while Robert Downey Jr. dons blackface as Kirk Lazarus, an award-winning white method actor who, in playing a black man, can't break character. Ever.

The three are on location in Vietnam, filming an adaptation of a memoir by war veteran Four Leaf Tayback (Nick Nolte, with hooks for hands, literally) that's being directed by some British guy (the ordinarily marvelous Steve Coogan, whose sole qualification for this job is an English accent). They're all watched over by an overweight, disgustingly hairy bulldog of a studio exec who's so foul—and foul mouthed—that you can practically see stink lines wafting off the screen.

Tom Cruise plays the studio exec.

If you can't tell already, there's entirely too much going on here: Tropic Thunder wants to be a comedy and a slam-bang action ride, but the violence is too grisly to be funny, and the concepts keep folding in on each other. Shit goes wrong quickly, and soon the actors are stranded in the jungle, thinking that hidden cameras are filming them, while in fact the very real explosions and bullets are from a group of Vietnamese heroin manufacturers.

After an intensely long setup, and introduction of premise after premise (Black's character goes through a harrowing withdrawal! Matthew McConaughey is Stiller's agent! Tom Cruise dances like Dr. Evil! Robert Downey Jr. still thinks he's black!), Thunder finally hits truly surreal, absurd proportions. Smiles slowly begin to form as Downey's jive utterances start to reveal something about his actual character; incredibly likeable supporting actor Jay Baruchel (Undeclared) becomes the movie's sole voice of reason; Cruise's faceoff with McConaughey is played for intensity, which totally works. When Stiller is forced by the drug army to reenact his least successful film role as a retarded farm hand, and Jack Black is hogtied to a water buffalo half-naked, Tropic Thunder finally makes good on all that painstaking preparation.

But good lord, it takes a long time and a ton of explosions to get there.