I have been obsessed with Loki from the movies Thor and Avengers. I think that Odin screwed Loki over by keeping the truth from him. Loki had a hard time in Asgard since no one trusted him and thought the worst of him. They always overlooked him and his victories. They would look at Thor's victories which probably only happened because Loki would use his magic to save their asses.  I feel like people treated Loki bad and eventually he just snapped.

I believe in Avengers Loki was under mind control. His eyes are green and not blue; the Chitari could have used the scepter to mind control him. While I believe Loki normally would be strong enough to resist it, but given the circumstances of him falling from the bifrost and being in a dark place it would have been easier for them to control him. 

I hope in the following Marvel movies with Loki in them , Loki is redeemed because I don't think he is a evil person by heart just misunderstood.