I never really cared for Sirius, and his character was never fully fleshed out. In fact I got annoyed with the way Harry got obsessed with him after his "death" (lamest killing of all time).
I think the series is great, but I wholly expect there to be some deaths. Somehow Snape is going to be the hero in the end.
I'm with you- I cant believe the headmaster had so much faith in Snape, and it was unjustifued.
I hope he comes through in the end and it is shown that it was all a plan to help kill 'you know who'
She can't just leave the story with Dumbledore being a dead clueless rube. It's all a game and Voldemort's going to fall for it.