Big laughs are to be had in this rip-roaring Hollywood satire, directed by Ben Stiller. Tropic Thunder may not quite match modern classics in the same vein, like Team America or Galaxy Quest, but the entertainment factor is dialed up high.

Ben Stiller plays Tugg Speedman, a failing macho star whose last chance at glory is playing the lead in Tropic Thunder, a grandiose Vietnam actioner which in fine retro-Coppola style is going seriously over budget and over the top in its jungle location. Tugg is playing opposite the Australian method actor Kirk Lazarus (Robert Downey Jr) who has the role of the African-American sergeant. Kirk has caused some unease by having a special dermatological operation to turn his skin black, and never comes out of character, speaking throughout in a quaint late-60s grunting jivetalk, which he appears to have learned from the Chicken George character in Roots. This enrages the genuinely black actor in the cast, Alpa Chino (Brandon T Jackson), a hip-hop star whose silly name incidentally is based on but does not satirize Al Pacino's existence or style in any meaningful way.

When the cast gets lost in the jungle and kidnapped by a paramilitary drug gang, Tugg is convinced these people must be actors playing Viet Cong and the whole thing is some kind of hidden-camera improv challenge. Catastrophe looms when his captors demand a ransom from studio boss Les Grossman played by Tom Cruise as a horrifically fat, bald monster - and Grossman realizes that by simply letting them kill Speedman, his studio can collect a mind-blowing insurance payout, turning this certain flop into a monster profit.

Poor Tugg is hurting inside because his previous film was an attempt at a human-interest drama, Simple Jack - in which with excruciating lack of taste he plays a young man with mental disabilities. It died horribly at the box office. Kirk tells him why: "Never go full-retard. You should only go part-retard to get an Oscar. Think about it: Dustin Hoffman in Rain Man - part-retard. Tom Hanks in Forrest Gump - part-retard. Peter Sellers in Being There - part-retard. Just part-retard to let the audience in. But Sean Penn in I Am Sam? Full retard!"

At this moment, Stiller goes for full-satire; maybe part-satire would have soothed the protesters. But it wouldn't have been as funny and we would have lost out on some acute film criticism. Tropic Thunder isn't a masterpiece, but it is supremely effective entertainment.