Your enjoyment of the second Thor movie will depend on 2 things:
1. How much you enjoyed the humor of the first movie
2. How much you enjoy Tom Hiddleston as Loki
Like Iron Man 3, Thor: The Dark World picks up soon after The Avengers. Loki (Tom Hiddleston) is returned to Asgard in chains and Thor strives to keep the 9 realms safe. Jane Foster (Natalie Portman) has been pining away for him while visiting a mentally unbalanced Eric Selvig (Stellan Skarsgard). But Jane stumbles upon an ancient weapon known as the Aether which is sought after by Malekith (Chris Eccleston), leader of the Dark Elves, who plans on using the Aether to plunge the entire universe into darkness.
There are a number of improvements over the first Thor in the sequel. The chief among them is scope. Whereas the first essentially only had 3 locations (Frost Giant World, Asgard, and New Mexico), this new story crosses many of the 9 realms. We also get an expanded view of Asgard, which is given a lot more tangibility by the production design. It feels like something more like something out of Lord of the Rings than The Phantom Menace (though there is still heavy use of CGI here).
The action sequences are also more exciting than the first. They are bigger in scale and a bit more creative. In addition, I really dig the design for the Dark Elves' technology. Their attack ships have a sleek, non-symetrical design that is so funky I couldn't take my eyes off of them.
The performances are a mixed bag. Hopkins phones in Odin even more-so than the first movie. And Kat Denning's Darcy is nothing but snark in a crocheted hat. But Hemsworth brings more maturity to his Thor than the last time. You can see the interior difference in the character. Portman is believably love-sick. The Warriors Three have more screen time and have a chance to show a bit more charm and subtlety. Renne Russo's role as Queen of Asgard Frigga is expanded greatly over the last movie. And Eccleston does a fine job as the malicious Malekith.
Regarding Hemsworth, I particularly like watching him struggle between his duty as future king of Asgard and his affection for Jane. The difference in their lifespans looms over them and he is constantly reminded of that parting which will come sooner than he would like. The movie also hints at a love triangle between Thor, Jane, and Sif (Jayne Alexander). I would have liked the movie to delve more into that relationship, but director Alan Taylor is content to hint at it with looks and gestures.
But it is Hiddleston who steals the show. Every scene he is in, he draws you with his charisma and biting humor. You cannot help but like him even though he is a mass murderer. You can see his brokenness hidden behind illusion and quips. He is written much differently than the first movie and reflects the Whedonesque tone he found in The Avengers. Unlike Denning's performance, Hiddleston uses the humor to get you deeper into his character. One of the great things about how they use his character is that even as you like him, you feel like he is setting you in a trap. And you just don't care.
The most interesting thing about the movie is the tonal bounce. There are moments that are meant to be profound, shocking, and heartbreaking. But very quickly the movie will break in with a gag to releave the tension. Even in the middle of the final action sequence, the movie would pause for extended jokes. This almost throws movie off the rails. If the film treats the threat like a joke, so will the audience. But it never quite crosses that line, even though it move dangerously close.
And as I said at the beginning, your enjoyment will depend on your reaction to the humor. I've picked on Dennings here, but even though she is one dimensional, I did not find her that annoying. In the same way, if humor of the first movie turned you off, you will not like this movie. But if you found that it gave the film a fun vibe, then you will enjoy Thor: The Dark World.
4 out of 5 stars.
(One more thing: as a comic book geek, the first after credit scene blew my mind with the realization of the story lines to come and the fact that those elements had been in front of me the entire time. I cannot say more without spoiling)