Fresh from Cloud Atlas, nonthreatening young nouveau-matinee-idol Jim Sturgess leaps straight into yet another lumpy, draggy, poorly written science-fiction romance thing. This one’s a story of forbidden love between the class-stratified peoples of two adjacent planets with opposite gravities and only a single sinister corporate office tower connecting them. Obviously Sturgess’ love interest must be played by Kirsten Dunst, movie-proven doyenne of upside-down kissing. Together they’re totes adorbs, but what a clunky, cloying mess the story is. Writer-director Juan Solanas hails from Argentina originally, and his whole film seems like one big loss in translation. Maybe some attempt at compensation is why the actors, including Timothy Spall in an awkward and unnatural supporting role, overinflate themselves with goodwill. As accidental camp, at least, Upside Down is not without potential: One plot point involves face-lift cream made with an old family recipe for gravity neutralization; another hinges on the hero unwittingly pissing on the ceiling. The climactic chase scene seems ripped off from some aggressively whimsical video game. But at least it’s a really original concept, you may think, unless you saw the animated short film Head Over Heels, an Oscar nominee from last year, which did it better, in a tenth of the running time, with puppets.