Well, how far have you gotten? I guess it was a big shock when Snape killed Dumbledore, but the big question in the 7th book was whether or not Harry would survive. When I first read the 6th book, Snape killing Dumbledore shocked me. I don’t know how surprising it would be to someone reading the books now for the first time, since they’re so well known at this point.
That part about the Deathly Hallows isn’t a big part of the story. It’s an old fairy tale or fable mentioned in the book. Knowing that won’t ruin anything for you. And sorry, I guess I answered with the assumption that you’d read all of the books!
I missed the part of the question about not taking Snape off to prison. There isn’t a lot of talk about that in the books, but I think he sort of went into hiding with the other Death Eaters at the end of the 6th book. If you haven’t read the 7th book, I don’t want to say too much else about it at this point. I actually typed out a whole explanation before I realized I was getting into the plot of the last book!