Among the Avengers, Thor should reign supreme. Sure, Captain America is the leader, but even he's just a jacked-up human. Thor is a god, a flying titan with a 5,000-year lifespan. Which explains why he's befuddled when Earth girl Jane (Natalie Portman) slaps him for ditching her in New Mexico. To her, the blond lug (Chris Hemsworth) has been MIA for two years. To him, it's just been a pop-off while he fought the rest of space into submission. Though Portman and Hemsworth are two perfect physical specimens, they give off less heat than a dime-store lighter. No matter. Their miscast romance is just one cog in Thor: The Dark World, itself just one motor in the billion-dollar Marvel machine that will run as long as each film is competent. The Dark World has the essentials: four fights, six quips, one city reduced to rubble. Instead of Kenneth Branagh's delightfully silly Shakespeare, this Thor is helmed by Alan Taylor of Game of Thrones. Thor's astral home is twinklier, the Rainbow Bridge is rainbowier, and the villains, well, are still grim-faced aliens -- haven't we killed six kinds of them already? --equipped with yet another raw element of destruction. Hemsworth's Thor gets one half-decent nude scene, though nothing so lusty as in the first film, when he silenced Portman just by passing shirtless through her apartment. The sequel forces him to spend most of his time in space, against CG vistas that leave him seeming puny. He fares better on Earth, where Hemsworth gets laughs in mundane surroundings, dutifully hanging his hammer on a coat rack. Torn between two worlds, the character feels adrift in his own movie.