Thor 2 is a pretty epic movie but it has been eclipsed by the amazing Marvel movies that followed it. Guardians of the Galaxy and Captain America 2 were utterly phenomenal and this movie did have some issues.
I think generally the issues with it are villain development and also trouble juggling the Earth characters with the Asgardian characters.
I have heard a lot of people critisize the battle with Malekith but I actually think it was really awesome. The two are battling across different dimensions, flowing in, dropping, jumping all while fighting with each other. I do agree that more time could have been spent developing Malekith, but this scene itself is pretty sweet.
I also think the special effects and visuals on the Attack on Asgard scene are some of the best in any Super Hero movie.
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