The above paragraph could describe one of a million sequels, but this week it describes The Hangover Part II, an underwhelming but not appalling effort to top the surprise smash of summer 2009. Although the original Hangover is no classic, the production seemed blessed with some sort of comic kismet, arriving at exactly the right time and place, with the brunt of the weight not on the script but inspired group casting and top-notch riffing. Although some of that peeks through in Part II, the film feels like an earnest punch pulled back mid-swing, unable to truly set itself apart from its predecessor.

Some time after the fateful Vegas incident, Stu (Ed Helms), Phil (Bradley Cooper), and Doug (Justin Bartha) are all ready to fly to Thailand for Stu's wedding to his new girlfriend Lauren (Jamie Chung). Fearing a repeat, Stu refuses to have a bachelor party, and doesn't have an invitation for Alan (Zach Galifianakis) until Doug's wife Tracy (Sasha Barrese) applies a little pressure on Doug on her brother's behalf. A half-day flight and one awkward dinner later, the foursome hit the beach to toss back a (roofie-free) beer with Stu's future brother-in-law, sixteen-year-old Teddy (Mason Lee), and everything seems fine, but when they awake in the morning, it's an even worse version of a familiar scene. Alan's hair is shaved, Stu has a tattoo on his face, and they're sharing their Bangkok hotel room with a monkey in a denim jacket.

Let's start with the good first: there's something to be admired about the way The Hangover Part II takes the extreme events of the original, which are intense yet fun in a heightened, exaggerated, "we got drunk and did something stupid" way, and replaces them with a night of debauchery that really crosses the line into dark, scarred-for-life territory. The glossy, photogenic sheen of the Vegas nightlife is replaced by the grimy, slummy back alleys of Bangkok, which feel both dangerous and sweaty -- the whole city appears to perspirate. Todd Phillips and his co-screenwriters Scot Armstrong and Craig Mazin are also good about keeping the balance intact: The Hangover Part II remains an ensemble, with Stu as a backbone, and the mystery (which doesn't involve Doug, but Mason) is well-executed and approximately as clever as the original's twist.

Still, the shadow of the original looms large. When the trailer hit, the general consensus was simple: The Hangover Part II looks like the same movie. Before seeing the film, it was easy to brush the criticism aside; of course it looks like the same movie, it's a sequel, and by nature, it sort of has to, doesn't it? Sadly, the criticism is more accurate than expected. Take the first five minutes: people setting up a wedding, the bride wondering where the group is, a call to Doug's wife, Phil telling her everything's gone wrong. Beat for beat, the film feels like Phillips and company opened the screenplay for The Hangover and wrote new jokes over it on a scene by scene basis.

The basic problem with the film's similarities are obvious, but there's a more subtle problem at work. Comedies thrive on atmosphere, and of anything most sequels fail to re-capture, atmosphere is the most important element. As with most memorable comedies, The Hangover is funny not just because it's well-written, but because it generates a mood or air of humor even when the script isn't offering up actual gags. The sequel, in its need to be similar-but-different, inadvertently ends up with more delineated set-up and punchline gags, with all of the dialogue and action falling into one of the two phases. Alan's "masturbating baby" pantomime from the first movie is funny and spontaneous, but you can't script a moment like that and have it be half as effective.

Phillips indulges himself in a few scenes, particularly a bizarre flashback/dream sequence in Alan's head that's more weird than funny, and the script leans on Ken Jeong's returning character Mr. Chow far too much for its own good. The film tries its hardest to subvert the expectations of an audience familiar with the first movie, but the twists end up doubling back on themselves to become the same old gag. The Hangover Part II is far from a disaster, but it's also hard to imagine the film being any better than it is. Maybe "What happens in Vegas, stays in Vegas" wasn't such bad advice after all.