Starting out with promise, like a glossy, heated, modern-day film noir tribute, this thriller eventually begins to reveal its twist, and everything that was working until then simply collapses. Written and directed by Steven Knight, who usually specializes in dark, noir-like stories (Eastern Promises, Locke, etc.), Serenity goes in a more science fiction-y direction, and several things fall apart. For one, the heightened performance style, presumably borrowed from classic movies like Double Indemnity, stops working as well within the new context. It becomes difficult to care about the characters, and the actors' oversized performances are somewhat silly. (Only Hounsou somehow hangs on to his dignity.)
And the entire film noir concept, with its sex, booze, and murder, doesn't make any sense when the twist comes; it's actually somewhat icky in context. Even the twist is handled poorly. Rather than saving it for a jaw-dropping moment at the very end, it's slowly foreshadowed (through odd cuts and camera movements and some dream/nightmare sequences), revealed early, and explained extensively, without leaving even the slightest possible hint of ambiguity about what's really going on. There's no mystery. The island scenery is appealing -- with occasional lightning storms adding atmosphere to the bright island air -- and Hathaway makes a great femme fatale. It's too bad Serenity couldn't have been a straight-up film noir from start to finish.