But he still has a lot to learn about character development and fashioning a satisfying narrative.
Here he plays Peter Bretter, a big soft (in both the physical and emotional sense) homebody who writes music for TV shows and has for the last five years been the boyfriend of hottie actress Sarah Marshall ( Kristen Bell), star of a "C.S.I."-type show called "Crime Scene: Scene of the Crime."
Early in the film Peter, fresh from the shower, is visited by Sarah, who announces she's breaking up with him. Segel plays the scene in the nude. Like totally. Talk about vulnerability.
He mopes. He cries. He scores with a girl he meets in a bar, but instead of a post-coital cuddle he bawls into his pillow. The guy's a mess.
Finally he decides to get away from his woes by vacationing at a posh Hawaiian resort - only to find that Sarah and her new boyfriend, pompous British rock star Aldous Snow (Russell Brand), are checked into the same hotel.
Peter is so clearly humiliated, so obviously squirming on the hook of unrequited love, that a cute hotel clerk named Rachel (Mila Kunis) takes pity. She comps him a lavish suite well out of Peter's price range, and then allows him to tag along as she parties with other hotel employees on the beach.
Indeed, the entire resort staff seems to adopt the sad sack Peter. And ... and ...
And that's about it. "Forgetting Sarah Marshall" has a workable if unoriginal setup, but as a story it's like one of those hotel guests sitting in an inflated inner tube and drifting in lazy circles. It doesn't really go anywhere.
Which is a problem with a romantic comedy, because if nothing else you want to feel like you're part of the romance. What we get mostly from this film is ambivalence.
The essence of drama is conflict and change - and nobody changes much here. Certainly not our leading man, a sort of human marshmallow who's as bland at the end as he was at the beginning.
Nor can director Nicholas Stoller (who had a better script for "Blades of Glory") give much shape to this material.
There are some pretty funny lines delivered by a host of familiar faces: Jonah Hill (of "Superbad") as an unctuous hotel waiter, Paul Rudd ("40-Year-Old Virgin," "Knocked Up") as the resort's stoned surfing instructor), Bill Hader ("Superbad") as Peter's exasperated brother, Jack McBrayer ("Walk Hard" and TV's "30 Rock") as a honeymooning groom unmanned by his bride's sexual demands.
The real find here is Brit actor Brand as a rock idol who's lived the high life for so long he's forgotten what normal life is like. He's a silly wanker, yes, but still rather a decent chap beneath his ridiculous wardrobe and womanizing ways.
Unfortunately, few of the laugh lines go to the ladies. Bell ("Veronica Mars") and Kunis ("That '70s Show") are used mostly as straight men - er, women - and attractive window dressing. C'mon guys, let the girls be funny, too.
See the trailer and find local showtimes for "Forgetting Sarah Marshall."