My own view on Snape: I think he's one of the good guys, and his severe dislike for Harry is a little contrived. Didn't one of the books say that either James or Dumbledore saved Snape's life? There's a story there we don't know yet. I'm thinking Snape has been working as a double agent for Dumbledore all along. His killing Dumbledore, strange as it sounds, was likely on Dum's orders, something like "If Draco does corner me and can't kill me, you do it"... again, there's something going on here we don't know yet. I think Snape will play a role in bringing down Voldemort and it will be revealed that Snape doesn't hate Harry as much as it has seemed, although he probably doesn't think he's all that cool either. After all, Harry isn't James and is a lot more humble. Still, in OOTP, when Harry snuck a look at Snape's memory in the pensieve, that was probably a genuinely angry moment...