Three out of Five stars
Running time: 107 mins

Enjoyable comedy with terrific performances and several hilarious gags, but the plot loses its way halfway through and it runs out of steam before the end.

What's it all about?
Action hero Tugg Speedman (Ben Stiller), fat-suit-loving fart gag supremo Jeff Portnoy (Jack Black) and Oscar-winning Australian method actor Kirk Lazarus (Robert Downey Jr) are uniting for the first time to make a Vietnam epic for studio boss Les Grossman (Tom Cruise). They dutifully pile into the jungle along with a neurotic British director (Steve Coogan), the grizzled author of the book the film's based on (Nick Nolte) and an over-enthusiastic explosives expert (Danny McBride).

However, due to a misunderstanding, the actors find themselves slap bang in the middle of a real rebel attack and assume that they're being expected to improvise in front of hidden cameras. And as if that wasn't bad enough, the director disappears into thin air (literally), a blackfaced Lazarus refuses to break character ("Ah don't break charactur until ah finish the DVD commentary!") and Portnoy is struggling with a massive drug habit.

The Good
The film starts brilliantly with a series of entertainment reports and trailers that introduce the characters and set the scene. The trailer for Lazarus' conflicted monk love story Satan's Alley, in particular, is a work of comic genius.

The three leads are all superb, with Downey Jr nabbing the lion's share of the laughs (particularly when offering Speedman advice on winning Oscars), while Cruise, McBride, Nolte, Coogan and Matthew McConaughey (as Speedman's agent) all shine in supporting roles.

The Bad
That said, the first half of the film is much funnier than the second and it loses its way quite badly about halfway through, becoming less and less amusing as the ridiculous action element takes over. It also gets a little overindulgent, with a couple of sequences that aren't nearly as funny as they're meant to be.

Worth seeing?
Tropic Thunder is hilarious in places and worth seeing for Downey Jr alone, but it's not quite as funny or as satisfying as it should have been.