This thin premise is better suited to a half-hour sitcom than a feature film (in fact, there's an episode of Frasier with a very similar setup), but it's strong enough to support some fun performances from a group of TV stars, along with a lot of weightless filler. Peter Bretter (How I Met Your Mother's Jason Segel) and Sarah Marshall (Kristen Bell, of TV's Veronica Mars) are the kind of cutely mismatched Hollywood couple that usually comes with an expiration date: She's Billy Baldwin's sexy costar on the popular forensic investigation series "Crime Scene: Scene of the Crime," he's the doughy composer whose ominous music accompanies the show's lurid revelations ("It's true: The killer did masturbate before each murder") as well as Baldwin's achingly unfunny ripostes ("Where he's going, he'll need to know how to masturbate"… huh?). They've beaten the odds for more than five years, so it's no wonder Peter is completely shocked when Sarah hands him an upgrade notice: They've grown apart, they've begun living separate lives, blah blah blah, and yes, there is a famous someone-else: Aldous Snow (Russell Brand), the pompous lead singer of Infant Sorrow, whose embarrassingly earnest anthem "We've Got to Do Something" is racing up the charts. Devastated, Peter first tries to forget Sarah with a series of meaningless one-night stands, most of which end in tears -- his -- but then he decides to listen to the advice of his half brother, Brian (Bill Hader), and get away from his memory-filled apartment. On a whim and without a reservation, Peter flies to Turtle Bay, the Hawaiian resort about which Sarah often talked and where, wouldn't you know it, she coincidentally happens to be vacationing with Aldous. Not wanting to look like a stalker but also unwilling to give Sarah the satisfaction of knowing he changed his plans, Peter stays put, even though the only available room is a lavish, $6,000-a-night suite he can't quite afford. When pretty concierge Rachel (That '70s Show's Mila Kunis) realizes what the heartbroken Peter is going through, she hands him the key to the suite gratis, as long as he promises to clean up after himself. Hawaii, however, is a small island, and the resort is smaller still: No matter how hard Peter tries to avoid Sarah and Aldous, they seem to be ubiquitous. The only way Peter will be able to forget his ex is with a new love: Rachel, perhaps? Written by Freaks & Geeks/Undeclared/KNOCKED UP's Segel – so committed a comic actor that he goes the Full Monty not once, but twice -- and directed by Undeclared writer Nicholas Stoller, this heartbreak-kid comedy is very much a Judd Apatow production: It even features Jonah Hill as an obsessed Infant Sorrow fan who works at Turtle Bay. He's just one of an array of supporting players -- Jack McBrayer as a Christian virgin on his honeymoon is another -- who pop up whenever the trifling main plot starts spinning its wheels, and that's pretty often. There are some good bits -- the "Crime Scene" spoofs are spot-on, Kunis is cute, and Brand is both perfectly cast and perfectly hilarious -- but like many other recent Apatow productions (KNOCKED UP, SUPERBAD) the rest could have used some tightening.