“Thor: The Dark World” opens Friday at Point, Eastgate and Star Cinema. PG-13, 1:52, two stars out of four.

Man, the screenwriters of “Thor: The Dark World” must look back with envy on the writers of the first “Iron Man” movie. Times were simpler back then — there wasn’t this whole interconnected Marvel cinematic universe of cameos and post-credit sequences and overlapping plots to pay fealty to. There’s much talk in “The Dark World” of the Nine Realms all coming into alignment for the first time in 5,000 years, but that’s nothing — try and keep nine superhero franchises lined up.

It’s that duty to the mega-franchise that really weighs down “The Dark World,” which is otherwise a slight improvement over its predecessor. Oh, it’s still dumb and lumbering, an ungainly mix of superhero film and swords-and-sandals fantasy epic. But its wits are a little quicker, with Chris Hemsworth finding the humor and charisma in his golden-maned hero, and the duplicitous Loki (Tom Hiddleston) getting some good lines.

“The Dark World” opens with Anthony Hopkins, as the Asgard king Odin, serving up a huge, nearly indigestible slab of exposition right from the get-go. Millenia ago, the evil Dark Elves, led by the really evil Malekith (Christopher Eccleston) tried to use a doomsday device called The Aether to destroy the universe. (Why? Just cuz.) Odin’s father prevailed, banished the Elves and hid the viscous Aether where he was sure no one would ever find it.

Yeah, right. Who should stumble across the Aether but, in a really strained attempt to bring back the Earthbound characters from the first film, inter-dimension traveling scientist Jane Foster (Natalie Portman), Thor’s old flame. The Aether hops into her body, which sets off Malekith’ snooze alarm, and he and the other Dark Elves all zoom to Asgard to get her.

To stop them, Thor enlists the aid of his villainous half-brother Loki, imprisoned for being the villain in “The Avengers,” and the two form an uneasy alliance. Loki’s presence was reportedly beefed up in the script after Hiddleston was such a hit in “The Avengers,” which is great, except it completely overshadows Malekith as the supposed main villain. And I haven’t even started on the other Earth characters (Skellan Skarsgard and Kat Dennings) trying to find Jane in London, including Skarsgard, his character still addled from Loki’s mind control, playing most of the movie without pants.

If that sounds like a lot to stuff into one movie, it is, but the real problem isn’t the clashes in story, it’s the wildly divergent clashes in tone. The scenes on Asgard and some other realm with the really unfortunate name of Svartalheim are deadly serious, full of portent. Meanwhile, the scenes on Earth are played for broad slapstick. Director Alan Taylor (taking over for Kenneth Branagh) just can’t reconcile the different tones. There’s a fairly major character death midway through the film that should be a somber moment, but it’s impact is completely robbed by cutting back to the wacky antics in London.

The visual effects are pretty but weightless, and the actors do what they can to make some kind of mark among the CGI mayhem. At least Hemsworth has settled nicely into his character — one of the best moments in the film occurs when he has to hop on the London Tube, crammed into the sardine can in full Asgardian regalia, and can’t help but flirt a little with a fellow passenger on the way to the latest Battle to Save Humanity. He’ll likely be better served by Joss Whedon and “Avengers 2.”