Just finished reading the book. It took me just under three and a half hours (my usual speed, 200pages/hour).
First, I do think that fandom had a major influence on my reading of this book. There were many things that didn't feel nearly as new or surprising because I'd seen them done so many times before in fanfic. But I still think that fandom's worth it.
Regarding Snape: I am 99.99999% sure that he was/is, in fact, loyal to Dumbledore and the Order. And I am not a Snape fan; I think he is a nasty person who has quite a lot of wrong-doing to account for, but I am sure of my view. I am sure that when Dumbledore was saying "Please" to Snape there at the end, he was begging him to kill him, and not to try to save him and thereby ruin all the plans they had no doubt made together. I shall have to put an essay together, gathering all the mentions of Snape in the book that make him seem like a traitor, to illustrate my point of view.
Regarding my fanfic.... This pieces-of-soul business makes things a bit complicated... I don't think it's realistic to have the fanfic continue from book six and just make minor changes to recognize the fact that Dumbledore died earlier than I had written.... On the other hand, instead of killing that last bit of soul once all the others are destroyed, maybe Harry can still use that Time spell to change Voldemort back to the way he was as a baby.... The question is, which is more powerful, the fact that parts of his soul were destroyed, or time itself? I shall have to think a bit about whether or not I want to continue my fanfic as is, as post book five, or to make a few changes and continue post book six....
And the title? Half-Blood Prince? I'm still not sure whether I think it was clever or just a bad way to try to get people to speculate - without ANY success - about what was meant by 'Half-Blood Prince'.