‘Thor’ borders on being a bore

For a semi-god who has traveled the universe and can pretty much beat the cape off any other force in any dimension with a magic hammer, Thor somehow always looks best when surrounded by little old Earth.

That was why the first stand-alone film based on the Marvel Comics character worked. Even though it represented the formulaic story line of a big fish stuck in a small pond, and even if Natalie Portman’s talent was wasted on a role that was much too small for her, it worked.

Now comes “Thor: The Dark World,” opening today, which is fun but hardly seems necessary. It’s like the Disney/Marvel machine has worked up such a giant head of steam releasing comic book movies that nobody has bothered to notice that some of the movies aren’t very good. “Dark World” could have waited a year or two while someone came up with a more original story.

That’s especially so, given that the comic book bar has been set so high in recent years with the Dark Knight and Iron Man franchises, not to mention the mostly successful Superman reboot.

Or maybe I’m just disappointed because Thor — again played with a convincing balance of might and mirth by Chris Hemsworth — never once uttered “it’s hammer time” before pulverizing a foe into dust.

The new chapter finds Thor back on his home planet of Asgard, when an ancient, angry race led by underexplained villain Malekith (Christopher Eccleston) re-emerges to plunge the universe back into darkness by destroying something known as the nine realms. It’s based on Norse mythology, and it’s complicated. And, frankly, the film could have used a better source of motivation. As it is, Malekith comes off as powerful sci-fi version of an angry 16-year-old punk rocker. Malekith wants to destroy the status quo and needs the dark matter Aether to do it. As it so happens, the Aether has attached itself to Thor’s girlfriend, Jane Foster (Portman, with a slightly bigger, sassier, yet still not-big-enough role this time around).

You can see where this is going. Thor reunites with Jane, whose outrage at Thor’s two-year absence seems pretty absurd, since she knows as well as we do that he was off saving New York in “The Avengers.”

Together they take on the bad guys, and it does not go well. But just when all looks lost — and when one’s head starts to hurt from all the splashy but overcooked special effects — the story resurrects its best character, Thor’s adopted brother Loki (Tom Hiddleston).

Hiddleston saves this movie. He’s become one of those actors — like Benedict Cumberbatch and, at one time, Gary Oldman — who can completely change the direction of an otherwise mediocre film.

In prison for his murderous rampage in “The Avengers,” Hiddleston grabs the second half of “Thor: The Dark World” and elevates it to the level of his talent. No one ever knows what’s motivating the sneering, sarcastic, patronizing Loki. He’s the greatest used-car salesman in the galaxy. You want to like him, you want to believe him, but he’s simply too smart and conniving to trust. His apparent emergence on the side of good this time allows for badly needed banter between the brothers that sets you up for a either a heroic transformation or a disappointing betrayal.

And, of course, Thor is always better on Earth, which plays host to all the devastation at the film’s climax. (That raises the question: Why not call on the other Avengers to help?) Though the movie’s outer-space special effects are pretty — almost too pretty — they tend to put the actors and the story on the back burner. Earth provides a better background to focus on what’s going on.

Unfortunately, what goes on at the end isn’t very original or even terribly interesting. And it’s only mildly entertaining, which is disappointing after Thor’s appearance in “The Avengers.”

Of course, you should stay through the credits to get your now-obligatory comic-book story surprise. It may be the only one in the entire film.

‘THOR: THE DARK WORLD’ (PG-13)

1 hour, 52 minutes.