At least the only character that really pissed me off in this one was Hermione, and even that was past halfway through the book.
Either way, nice enough, and the books in this series are certainly no longer children's books, only the first three could have been that, but... something in between now, not being quite complex or realistically harsh enough for the next step.
Have to admit my guess as to the identity of the Half-Blood Prince was wrong, but otherwise the ending was entirely predictable.

Spoiler

Would say the "good guys" emerged too... whole out of that situation; such a fight should have left far worse casualties.