Well, after waiting to read it unti after my Boards were done (which mirrored the O.W.L.s in a frightening way) I finally read the book.
I really, really enjoyed it. It certainly had some weak parts, but as mentioned, its just compelling. I couldn't put it down.
I really liked how much depth was added to a lot of the supporting cast. And Dumbledore rocked. I cheered aloud when I read his speech to the group when Fudge was arrested.
One loose end I would have liked to have seen tied up: Percy. When the very foundation of what he believed was right was rocked, what did he do? As much attention as he got I would have thought there would be at least a mention of him at the end of the book. Guess we'll have to wait until the next one.
I'm with Fell though, Snape is my favorite character...probably because he is one of the most three dimensional of all the cast.
As for Tonks and Harry...I think the age difference is a little much. Add on the few years before Harry graduates plus the three extra to become an Auror plus the fact that it was mentioned that the MoM hasn't taken on a new Auror is several years and it adds up to Tonks being in her mid twenties, at least.
I think I would like to see Harry and Luna get together as she has proven to be strange...but interesting.