Say this, "Thunder" is loud

You're going to read a lot about "Tropic Thunder," a new Ben Stiller-directed comedy about a troupe of actors making an out-sized Vietnam War movie. Moments of smart satire will be hailed as evidence of stunning cleverness, and intermittent laughs will become riotous explosions for those who see this send-up of Hollywood vacuity as something special.

I suppose you can tell from my tone that I didn't buy it, although from time to time, I laughed, and I certainly was fascinated to watch Robert Downey Jr. play Kirk Lazarus, an Australian actor who has had his skin dyed so that he can portray a black man in the movie-within-a-movie. It's one stunt in a movie that's full of them. Downey's playing the best actor in the movie, which comes across convincingly because Downey is the best actor in the movie. There's also a real black actor (Brandon T. Jackson) who takes appropriate offense at Kirk's portrayal. Jackson's Alpa Cino doesn't get the joke.

Although Downey somehow manages to survive this bizarre turn, "Tropic Thunder" has a hit-and-miss quality, as well as the head-splitting amplification of a real action movie, which it more or less becomes by the end. And, yes, Stiller probably could direct a real macho hunk of action. He evidently has the chops for it.

A buffed-up Stiller appears as Tugg Speedman, an action-movie star whose career is foundering. Perhaps tiring of his role as a kick-ass muscle man, Tugg tried his hand at drama. In his previous picture, he played Simple Jack, a mentally challenged man. Critics roasted the movie, and Tugg's performance was greeted with derision. Groups representing the disabled have complained about the movie's use of the word "retard." Stiller and cohorts may have wanted to shatter the boundaries of political correctness, but picking on the mentally disabled? The joke is supposed to poke fun at the lengths actors will go to in order to garner awards attention, but you can bet that some of the laughter will be directed at the Simple Jack character and not at Hollywood pretensions.

To up the comic ante, Stiller brings in some heavy comic artillery: Jack Black appears as one of the actors; Matthew McConaghey portrays an agent; and Tom Cruise has a weird turn as a balding, Jewish producer. Cruise's mini-perforance likely will win him some praise, but it seemed like one more stunt to me, memorable mostly because we didn't know that Cruise could be made to look this bad.

I suppose "Tropic Thunder" manages to hold our interest because there's a sense of danger about it, as if it's about to spin out of control. But like the action movies that it's attempting to send up, "Tropic Thunder" also can get on your nerves. Thanks to a bizarre contrivance, the actors wind up fighting real dope smugglers. To add to the movie's insane velocity, Stiller has hired Nick Nolte to portray John "Four Leaf" Tayback, the author of the book that's being filmed by Stiller and company.

"Tropic Thunder" has a wildly preposterous spirit, but it's not nearly as daring as it might want to be. Yes, it takes some shots at Hollywood, but in the end, this satire lacks a really important target. Many in the audience already believe that actors have swollen egos that spring from rampant insecurities and that Hollywood is full of phony-baloney exploiters who want to drub us over the head with one blockbuster after another. "Tropic Thunder" does nothing to disabuse anyone of the notion. In that sense, it's increasingly obvious -- and bound to be a hit.