Beyond the Abyss

"No, Loki."
Two words. They shattered him. There was nothing left, nothing at all, no chance left of gaining his father's approval, no hope of proving himself once and for all. His entire life, spent under the shadow of his great, would- be- king brother seemed to rush back on full force onto him as he dangled from the handle of the spear that had been passed onto his unworthy hands.
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At the end of the first Thor movie, we see Loki allow himself to fall into an abyss, anguished, broken and dismayed at his father's refusal to approve of his deeds. However, in his following appearance in The Avengers, he has become someone rather different from the schemer we knew previously; a vengeful, malevolent, ruthless invader. Was it really that he was merely driven by his jealousy towards his brother and hunger for power to become such a character? Or, perhaps... was there another factor to his villainy, something he had encountered during his exile?