As with the recent comedy-thriller "Pineapple Express," "Tropic Thunder" blends together explicit violence and bloodshed with what aims to be a hearty tide of guffaws. It's a curious mixture, not easy to pull off, but both of the aforementioned films do a pretty good job of making it work. The difference, then, is in the aftereffect. "Pineapple Express" treated the viewer to affable, at times even lovable, protagonists whose relationship was the building block for otherwise hit-and-miss material. By comparison, "Tropic Thunder" is a satiric spoof of Hollywood actors populated by shallow, dimwitted, self-absorbed characters. They are amusing in small doses, but no one would want to be around them for any substantial period of time. You certainly don't care about them, and so it's hard to ever warm up to the picture's intermittent pleasures.

"Tropic Thunder" is the title of a big-budget Vietnam War epic that has already gone overbudget after only five days of shooting. With cutthroat producer Les Grossman (Tom Cruise) threatening to fire director Damien Cockburn (Steve Coogan) if he doesn't pull it together, Damien conspires with Four Leaf Tayback (Nick Nolte), the vet whose non-fiction book the story is based on, to drop his actors off in the jungles of Vietnam as a way of adding authenticity to the project. When Damien accidentally steps on a landmine and is blown to smithereens, the central cast—fading action hero Tugg Speedman (Ben Stiller), drug-addled comedian Jeff Portnoy (Jack Black), Oscar winner Kirk Lazarus (Robert Downey Jr.), rapper Alpa Chino (Brandon T. Jackson), and newcomer Kevin Sandusky (Jay Baruchel)—is suddenly left stranded without direction. Believing it to be a part of their boot camp, the five of them journey deeper into harm's way, ultimately coming into contact with a community of narc-terrorists led by a 12-year-old drug lord (Brandon Soo Hoo).

Directed by Ben Stiller (2001's "Zoolander") and written by Stiller, Justin Theroux and Etan Cohen, "Tropic Thunder" is a smug comedy so blatantly pleased with itself that the finished product isn't nearly as much fun to watch as it probably was to make. When the film hits its target, the results are very, very funny, but most of these standout interludes occur in the first and third acts. The middle hour, with the actors wandering around in the elements with no real goal in sight, is by and large a dead zone that puts a halt to the energy created at the onset. The characters are all intentional caricatures, from the white method actor who has surgically altered his skin pigmentation in order to play a black man, to the out-of-control comic performer who lives his personal life on a steady diet of crack and heroin, and they remain that way for the duration. At no point does the viewer feel like they have grown into real people, and so there is a certain distance placed between the audience and the foolish figures on screen.

The best scenes are the very first ones, a collection of faux-movie trailers that put a delicious spin on the ripe clichés of modern-day Hollywood marketing (my favorite: a monks-in-love drama called "Satan's Alley," starring "Five-Time Academy Award Winner Kirk Lazarus and MTV Movie Awards' Best Kiss Winner Tobey Maguire"). Later, scenes glimpsed from Tugg Speedman's previous failed attempt to be taken seriously, a mental-disability hearttugger by the name of "Simple Jack," are so morally wrong that they're comedically oh-so-right. The inside humor revolving around the movie business is smart and tart, no doubt thanks to two of the screenwriters being seasoned actors themselves, but the plot, when it rears its ugly head, is meandering and close to lifeless.

In a supporting performance that is bound to receive more praise than it deserves, Tom Cruise (2007's "Lions for Lambs") shows up with a hairy fat suit and a bald cap in tow to play studio producer Les Grossman. Cruise curses like a sailor and dances to hip-hop tracks, but this is a gimmicky role that never takes off as intended and sort of leaves one shrugging. Better is the supporting turn from Matthew McConaughey (2008's "Fool's Gold"), having a ball and adding hints of depth to the part of Tugg's TiVo-enthusiast assistant Rick Peck. As for the leads, Ben Stiller (2007's "The Heartbreak Kid") and Robert Downey Jr. (2008's "Iron Man") get the best that the script has to offer, toying with relish their exaggerated characterizations. Downey Jr., sporting seamless make-up that transforms him into an authentic-looking black man, literally disappears and becomes Kirk Lazarus. Jack Black (2008's "Be Kind Rewind") has less to do as Jeff Portnoy, spending the majority of his screen time in a desperate search for a drug fix. He never rises above one note.

Comedy is a highly subjective art form—perhaps the most subjective of any genre—and so what might tickle one person's funny bone may leave a different person scratching their head about what all the fuss is about. With "Tropic Thunder," count me in the latter category. Laughs pop up on occasion, but they are interspersed with gags that fall to the ground with a thud and a whole lot of middling down time in between. The film's overriding cynicism and lack of a character to latch onto and care about cuts the potential fun in half. The ending, in which little is solved and no one learns anything, doesn't leave you rolling in the aisles so much as it sends you out with a queasy feeling in your stomach.