The story opens with a prologue because the director didn't have the confidence that his film would properly tell the story, which is a big red warning flag right there. We learn that the Dark Elves had a McGuffin and that they want it back in order to, [spoiler ahead] END THE WORLD. Were you surprised? I wasn't. About five minutes into the film, I felt bored. Although the film went on to amuse me, it never truly entertained me except as indicated above.
In this film, I learned that super-future worlds can't save people from gut wounds. Future weapons can't hit huge flying objects the size of buildings, nor can they coordinate. Nor can they think of anything better to do with prisoners than keep them in the capital, inside a vital military target. And when it comes to stories of the past, can't do much better than vague references in illustrated books rather than extensive treatises detailing one of the universe's most dangerous weapons just in case it should be used again, because, you know, obscure super-powerful weapons never get developed twice.
However, Thor: The Dark World does sufficiently succeed on the popcorn-o-meter that I can't wholey condemn it. As B-films go, and this was a B-film despite its budget, I found it sufficiently dorky and full of dorkness and it scratched all the appropriate itches, if imperfectly.