Segel's character, musician Peter Bretter, is a schlub, and it takes a little time to warm to him. Of course, we're not meeting him when he's at his best. The movie begins when Peter is told by his girlfriend - the titular Sarah Marshall (Kristen Bell), star of a lame "CSI" ripoff for which Peter writes the "dark and ominous" underscore - that their five-year relationship is over. Peter, who's naked at the time (and, yes, since Judd Apatow is the producer, we are treated to a full-frontal view), doesn't take the news well.

After wallowing in self-pity for weeks, Peter takes the advice of his brother Brian ("Saturday Night Live's" Bill Hader) and goes on vacation. When he arrives at an Oahu hotel, he's shocked to discover Sarah is there as well - with her new boyfriend, Aldous Snow (well played by British comic Russell Brand), a preening and much-tattooed rock star who is more hip than a dozen normal guys. The hotel's cheery customer-service rep, Rachel (Mila Kunis), takes pity on Peter and tries to cheer him up, turning a screwed-up love triangle into a farcical tetrahedron.

Segel and first-time director Nicholas Stoller are members of Apatow's posse (Segel was Seth Rogen's wingman in "Knocked Up," while Stoller wrote episodes of "Undeclared" and co-wrote with Apatow the failed remake of "Fun With Dick and Jane"), and like musicians they bring along familiar side men - notably Paul Rudd and Jonah Hill - who can be trusted to riff hilariously. There are other scene-stealers, notably "30 Rock's" Jack McBrayer and "Strangers With Candy's" Maria Thayer as a too-sweet honeymooning couple.

As a leading man, Segel (who also co-stars on the sitcom "How I Met Your Mother") is not causing Brad Pitt and George Clooney to lose any sleep. Doughy and a bit hulking, he looks more like the annoying pal of the character who gets the girl. But as a writer, he's written a perfect character for himself: needy, whiny but ultimately winning.

Segel has the Apatow gift for blending sweet and salty, mixing raunch with a romantic heart. And he knows to build to a climax, which "Forgetting Sarah Marshall" does with an outlandish musical finale - with puppets - that is, simply put, unforgettable.

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* SEAN P. MEANS can be reached at movies@sltrib.com or 801-257-8602. Send comments about this review to livingeditor@sltrib.com.