Here we have a showcase vehicle for Aldous Snow (Russell Brand), the vain, addle-brained British rock star who became the new boyfriend to Jason Segel’s TV-star ex-girlfriend in 2008’s Forgetting Sarah Marshall. Snow’s licking his wounds after his most recent record has become a critical and commercial flop. But a low-level music industry functionary named Aaron (Jonah Hill) has a notion that Snow can mount a comeback through a concert at Los Angeles’ legendary Greek Theater commemorating the 10th anniversary of a landmark live album by Snow’s band. All Aaron needs to do is squire Snow from London to a Today show appearance in New York, and then to the concert in L.A., all in 72 hours — a far-from-easy task given Snow’s fondness for altering his consciousness. Aaron’s a thinly drawn character as it is, a guy who has a big fight with his live-in girlfriend, Daphne (Mad Men’s Elizabeth Moss), just before launching a weekend of probable debauchery. Hill, fortunately, is about as innately funny as any movie comedian currently working, brilliant both when he’s freaking out in a Vegas hotel room on a multi-drug cocktail or when trying to maintain his dignity in a sports coat covered in his own vomit. But writer/director Nicholas Stoller (also returning from Sarah Marshall), just like his mentor Judd Apatow, wants to make sure there’s an emotionally resonant subtext to all the craziness. That’s frustrating enough when it’s just Aaron’s possible reconciliation with Daphne sucking up screen time; it’s borderline inexcusable when it’s also part of an attempt to “humanize” Snow. Brand is terrifically entertaining when he’s simply wallowing in Snow’s oblivious swagger. Turning his intoxicated excesses into a reaction to his break-up with a long-time girlfriend (Rose Byrne), and having him question the emptiness of his lifestyle, seems to miss the point of Snow’s appeal entirely. He’s supposed to be a shallow mess of a human being, not a wounded and multifaceted, sad clown. Complexity can only make the character less entertaining.