Malekith the Accursed is after the Aether, a powerful source of energy that he once possessed, that has the power to destroy the universe. The only thing standing in his way is Thor, and the mighty Asgardians, led by Odin.
What I loved about the movie was the use of Malekith as a villain who had a simple goal. He wants to destroy the universe. He knows what he needs to get the job done, and goes after it with great purpose and very little words. Malekith doesn't taught his enemies or give them long explanations. He simply sends his army into Asgard to fight, kill, and forgets all the questions you're supposed to ask later. He does very little bandying of words and never relents in his purpose. And boy does he have help.
!!! SPOILER ALERT: SOME SPOILERS BELOW, READ AT YOUR OWN RISK!!!
Long ago, Odin's father Bor was first to stop Malekith and his buddy Algrim. This time, Algrim becomes the being known as Kurse, and is given great power that none can withstand. Not even the mighty Thor, who he bats around like a baseball, after killing Thor's mother Frigga, a major turning point in the story.
Upon the death of Frigga, Odin in as expected, distraught and sad. Odin isn't thinking clearly and wants to fight the Dark Elves by luring them to Asgard. Thor on the other hand sees the error of this since Malekith is only after the Aether, which is locked inside of Jane Foster. He wants to lure Malekith to The Dark World to fight him there, to protect Asgard from Malekith's wrathful ambition. This is when Thor enlists the help of his adoptive brother Loki, who is a prisoner of Odin for his crimes against the realm and his attempt at being ruler of Earth. It is at this point in the movie where a good touch of comedy comes. The appearance of Captain America is both hilarious and so well placed that you go 'YES!', rather than saying, 'stop plugging Avengers in every Marvel movie'.
Can't Wait For X-Men: Days Of Future Past