Last things first: Do not leave your seats at the end of this movie. There are two bonus scenes awaiting you — the first adds a tag to the story, the second teases next year's Marvel space epic, Guardians of the Galaxy. By the way, the guy under the makeup in the final scene is Benicio del Toro.
Thor: The Dark World is the second film in the superhero series. It's ponderous at first, but gets better as it goes, with lively action segments and a good sense of humor. The film opens with the words, "Long before the birth of light there was darkness ..." Darkness, huh? As opposed to what? The sound of stubbed toes? An albino cave fish? The narrator went on to describe the backstory, which involves trolls or elves or something Lord of the Rings-ish. Whatever the critters are, they're pissed-off and planning to destroy or conquer pretty much everything. Yawn.
Don't worry, it gets better. Thor (Chris Hemsworth), he of the mighty hammer and bitchin' bod, has gone home. Papa Odin (Anthony Hopkins) is ready to make him King of Asgard (you remember Asgard — it's like the Emerald City, only more butch). But Thor doesn't want the throne. He pines for his earthly honey-bunny, astrophysicist Jane Foster (Natalie Portman). Odin is dismissive of the relationship. "Human lives are fleeting," he sniffs. Queen/mother Frigga (Rene Russo) is more understanding. Meanwhile, Thor's wicked, cool brother Loki (Tom Hiddleston) mopes in prison, and the majestic Heimdall (Idris Elba) guards the city.
Back on Earth, Jane, her wisecracking assistant/bestie Darcy (Kat Dennings) and Darcy's wide-eyed intern Ian (Jonathan Howard) — yes, the comic relief character gets her own comic relief character — discover a groovy anti-grav time-and-space transporter column in London. Jane's former mentor Dr. Erik Selvig (Stellan Sjarsgard) turns up on the TV news, running around Stonehenge naked and ranting. He joins the group later, working in a shirt and tighty-whiteys because he doesn't like trousers (Memorable exchange — Jane: "The very fabric of reality will be torn apart!" Dr. Selvig: "I better get my pants!").
The cast is strong, though Hopkin's Odin grows tiresome and sidekick Darcy, while amusing, seems to have wandered in from the set of New Girl. Hemsworth does a particularly good job, appearing bombastic and/or noble when appropriate while getting along nicely with his human pals. Though the villains-of-record are unmemorable, their threatened actions force Thor and evil Loki to team up, which makes for some dandy moments. Battle scenes are enlivened by holes in space and time which abruptly pop the warriors from one place to another. Neat!
Thor: The Dark World is uneven, but the combination of strong personalities, humor and clever battle choreography keeps the Marvel superhero movie formula from dragging.