So, after carefully reading what you guys are writing I'll jump in and give my perspective on the Loki character.
Loki is ambiguous, which makes it really difficult to actually be 100% sure that he has a certain intention or that he thinks A or B. In my opinion, Loki is a lot more complicated than being flat out evil and I think it shows clearly in Thor 1. He may be a trickster, but he is a person affected by what goes on around him and the way he grew up, positive and negative. Thor is shaped by the same mould and though he wishes to do the Right Thing he ends up taking actions that definitely can't be called heroic and good. It's not at all heroic to go to Jotunheim, start a brawl that leads to war (with Thor wanting to finish them off once and for all). It's not at all heroic to leave Bifrost open to tear Jotunheim apart either, as Loki does. Therein lies the disturbing truth that from the start, the difference between Thor and Loki isn't that great. It's not evil to be jealous, feel slighted and wish to prove oneself (Thor has some of these feelings too, though they are directed towards Odin), but it can lead to that individual making decisions and act in ways that leads to him/her doing incredibly evil things. This is also why it's so easy to wish to discard someone is evil, because we are all, given the “right” circumstances, capable of taking such a route in life. We just don't like to think we could. In that sense I find Loki's character quite tragic.
Also, I think it's reasonable that Loki is upset by Odin's admission that he thought Loki one day could be useful to him. It's a game of power and Loki is a pawn, the calculation of course being to have Loki on the throne in Jotunheim, and since he was raised by the Æsir, he'd be loyal to them first. That's the permanent peace Odin is talking about. I think anyone would have felt at least sightly used and betrayed, even if that person had grown up that close to real power. The question inevitably comes, do they really love me for myself, or am I just a tool to be used? Did I ever fit here or is everything just an illusion? And though Loki could have acted differently, the fact that he doesn't makes him quite human, with all the flaws we have, making the same errors. He is driven by resentment and a wish to prove himself and in the process he justifies his actions as being the best for everyone.
The fall he takes in the end is so metaphorical it almost hurts. The abyss is not just an abyss but also a moral and a psychological one, where anger and resentment can grow in to hate, driving him to revenge. I think he was easy pray in that mental state for anyone with ideas in the direction of conquering the realms, throwing logs on the fire in Loki's mind, trying to foster a useful tool.
Quite Shakespearian, the whole thing.