Tropic Thunder, starring Ben Stiller as one of a group of runaway actors whose work on a big-budget Vietnam epic goes horribly awry, is a funny, far-fetched mockery of modern Hollywood; the laughs don't maintain anything like a coherent intensity, but when they come, they're big enough to get you through the spaces between them. Some will mistakenly call Tropic Thunder a satire, but Tropic Thunder is in fact an example of satire's boisterous, bumbling sibling, the spoof. A satire's held with a light but precise grip, so the point can slice and the blade can cut; a spoof's more of a club, landing with blunt force and broad impact.

Star and director Stiller attacked the celebrity-industrial complex before, in 2001's Zoolander, and Tropic Thunder has more in common with that film than you might think; Stiller manages to mock action and thrills while also delivering them, and he's got a fine grasp of coarse celebrity behavior. Stiller seems drawn to characters whose self-centered arrogance is mixed in equal measure with self-loathing insecurity. We see an interview clip where Stiller's character, box office star Tugg Speedman, is informed by an interviewer how "Someone close to you said 'One more flop and it's over for him.'" Speedman pauses, and then asks his follow-up: "Somebody said they were close to me?"

Speedman's not the only flawed thespian flailing through the jungle on the set of the Vietnam epic Tropic Thunder, though. We also meet Jeff Portnoy (Jack Black), the star of several makeup-and-fatsuit blockbusters who's hoping to add some heft to his resume, even though shooting a war drama has him far from both his comfort zone and his heroin dealer. There's also Kirk Lazarus (Robert Downey, Jr.), an Australian five-time Oscar winner whose eagerness to take on a centerpiece role in Tropic Thunder has led him to have his skin darkened with an experimental medical procedure so he can play an African-American sergeant. With a rapper-turned-actor, Alpa Chino (Brandon T. Jackson), and eager young actor Kevin Sandusky (Jay Barcuhel) rounding out the cast, the Thailand production of Tropic Thunder is overblown, over budget and nowhere near over. Director Damien Cockburn (Steve Coogan) doesn't know how to put things right, and studio head Les Grossman (Tom Cruise, uncredited and nearly unidentifiable) is furious. But John "Four Leaf" Tayback (Nick Nolte), the real soldier and author Speedman's playing in the film, convinces Cockburn to get real, get raw -- and plunk the actors in the middle of the jungle, surrounded by hidden cameras, so they might break away from big-set conveniences and privileges to truly live, act and feel as these characters. It's a bad idea, and it gets far worse.

It's worth noting, though, that Tropic Thunder is what it mocks: Tropic Thunder's director of photography is John Toll, who's previously lensed Braveheart and The Last Samurai; production designer Jeff Mann has previously created big-budget eye-candy like Mr. & Mrs. Smith and Transformers. As a director, Stiller's crafted a big, shiny comedy, and the scale is, for the most part, matched by the laughs. There are nice side-notes from the supporting cast, like Danny McBride's short-fused explosives expert, or Matthew McConaughey's craven, cajoling agent, and Baruchel and Jackson get some nice moments in, also giving Stiller and Downey something to bounce off of. (Jackson and Downey have an exchange involving Lazarus taking offense at a perceived racial slight, followed by Chino taking offense at Lazarus's offense; it's brief, brisk and brilliant.)

And yet, the film belongs to its leading trio. Stiller's Speedman is an absolute idiot, but successful enough that his whims are law, and close enough to the edge of failure that there's a chance he'll topple over. Black's Portnoy, trapped in the throes of heroin withdrawal, is shameless and pathetic. Downey, though, outshines both his fellow leading men. Much has been made of Downey's playing a character in, essentially, blackface, but it's the rational irrational extension of every performer who's lost weight, gained weight or undergone some other radical transformation to play a role; it's not so much that there's a method to Lazarus's madness, but rather that his madness springs from method acting. As events spiral out of control, Speedman pleads with Lazarus to quit playing a part, even for a second. Lazarus's reply -- "I don't break character until I'm done recording the DVD commentary ..." -- is as inside as it is hilarious. It should be pointed out, though, that even with Tropic Thunder's many highly-charged elements -- Lazarus's dyed, bewigged transformation; the discussion between Lazarus and Speedman about how there's only a certain level of developmental disability the Academy will reward with an Oscar, and how Speedman crossed the line with his film Simple Jack when he "went full retard"; even the Vietnam War setting of the film within the film-- that Tropic Thunder is not making fun of race or retardation or the Vietnam War themselves, but rather the way a money-mad, success-chasing film industry turns every human challenge or historical tragedy into more grist for its mill.

Eventually, though, Tropic Thunder goes into action mode, with our cast stumbling across a heroin dealer's lair in the jungle. And Tropic Thunder stays funny, but I can't help but think that, as noted above, Tropic Thunder is what it mocks -- a huge, star-studded movie with explosions to hide the silences that occur when there's nothing else to say. Stiller, Justin Theroux and Etan Coen wrote a high-concept comedy, and at a certain point, the film's transformation to a high-concept action film is inevitable, as if someone thought that there needed to be a little loud noise and comedic violence to counter the deadpan quiet of the film's showbiz jokes and jabs. There are also plenty of logic holes in the film, too, but you're not going to look for them any more than you'd read the nutritional information on one of those fake canisters of nuts that has a fake spring-loaded snake coiled inside. I liked Tropic Thunder; I laughed, I wandered out happy -- but I had a vague, mild feeling of unease about it that crystallized a few days later when I read the Entertainment Weekly interview with Black, Stiller and Downey that closed with Stiller noting " ... you can't really do a sequel to (Tropic Thunder)" and Downey offering "Hold on. Let's see the numbers. If the numbers come in like we're expecting, we can at least talk about it." Tropic Thunder wants to make big money mocking big-money movie making, and the only thing that detracts from the fun and comedy is how, even while you're watching it, you can't help but notice the order those priorities come in.