I like the right ending, which isn't always happy. Sometimes, though, I'm specifically looking for a happy ending, so if the book doesn't deliver it, it's a matter of expectations. I don't expect happy-happy from literary fic, contemporary fiction, literary historical, or a book in the middle of a trilogy, for example. I do expect it from a fairy tale or MG (although even extremely literary, depressing MG often resolves itself in bows that are sometimes too pretty and uplifting).