Nothing gives me greater respect for an author than having the courage to end a book badly. That is not to say they ruin an otherwise good book by ending poorly. I mean when they stray away from a customary happily-ever-after and allow an alternative solution. When the girl doesn't get the man she loves. When the happy couple dies young. When the hero saves everyone but himself. When good intention becomes miscommunication.
After all, what is realistic about a fairytale ending? It's depressing really. It sets an absurd expectation that real life should some how parallel the blissful sunset scene. And when it doesn't, the fuzzy feeling accompanying a good book fades into resentment. But bad endings have a way of stirring things up
Of course, this can't be done carelessly. It has to be done with purpose. And it has to have some other form of resolution.
With the exception of Romeo and Juliet, I love the Shakespearean tragedies. (And Romeo and Juliet has some great lines and some really wonderful adaptations, but I just can't take them seriously). Shakespeare had a gift for knowing when to kill everyone to make a point.
How can you trust an author who never kills off a main character. You can attack the hero with any combination of calamities and hang them suspended in the most impossible circumstance. Your reader will breath easy. The character is safe. But have the courage to brutally kill someone the readers love and you will have earned their fear, and ultimately their respect. And that is the beauty of a wonderfully bad ending.