I don’t like novels or short stories where the author deliberately withholds stuff from the reader.
I’m not talking about mysteries, where part of the fun is in the puzzle and in the timing of the revelations; also, part of the thematic point of most mystery novels — even more than questions of innocence and guilt and justice — is the revelation of truth. I’m talking about stories where there is something significant about one of the characters, or about some aspect of the general milieu of the story, or about the resolution, that the author clearly knows but doesn’t choose to tell, instead toying with the reveal like a fan dancer in the burlesque.
Stories where the gender of the main character or first person narrator is kept hidden — especially if it’s revealed, gotcha!-fashion, at the end — are a particular irritant as far as I’m concerned. This, I will admit, is mostly a matter of personal taste, since I have known discriminating readers for whom such stories were like catnip to a Siamese. And it’s not even an absolute thing with me; I’m quite fond of the mystery novels of the late Sarah Caudwell, who never did reveal the gender of their first-person narrator, Professor Hilary Tamar. (I always pictured Professor Tamar as looking rather like an anthropomorphic sheep as drawn by Sir John Tenniel for a missing scene from Alice in Wonderland . . . in the absence of data, the human mind does strange things.) But Caudwell is a case of good writing plus good story trumping almost everything else; but a story that isn’t top-notch in both those areas is going to lose me before it goes very far.
Almost as irritating, where I’m concerned, are stories where the resolution is left open, in “The Lady or the Tiger” fashion, especially when the story seems to be offering the reader a deliberate ambiguity in order to establish some sort of literary street cred. Again, some people find endings like that to be right down their alley; I’m just not one of them. Instead, such endings make me cranky and resentful, because I always suspect in my heart that the author knows the true ending and is deliberately holding out on me — I think it’s because, as a writer, I can’t imagine not knowing the true ending of something I’ve written.
The moral of the story, if there is one: Don’t ever be accidentally ambiguous. If you’re going to do it, do it on purpose, in the full awareness that you’re probably going to lose some of your audience that way, and in the firm belief that whatever you’re trying to do or say with your story is worth the risk.
Dr. Doyle's Blog 
Almost as irritating, where I’m concerned, are stories where the resolution is left open
I can’t stand Crouching Tiger, Hidden Dragon for this reason. The ending feels like a test where you ‘deserve’ a happy ending if you believe in magic, and get stuck with a tragedy if you don’t. In my view, however, it’s the creator’s responsibility to make me believe that any given kind of magic is real in their world.
For me, it’s not that I assume the writer knows and is holding out; I assume they got to the end, realized they didn’t have a conclusion, and decided they could be ‘literary’ by expecting the reader/viewer to write their own.
So I’d say, even if you are being deliberately ambiguous, think it’s worth the risk, etc, make sure you actually set up the question before the reader/viewer needs to wrestle with it. And set it up right, so that all of the ambiguous choices you present feel plausible. If you have a world where magic is subtle and mostly involves super-powered fighting skills, a few lines about a legend that people can throw themselves off a cliff to make their dreams come true is not actually sufficient setup for throwing a main character off a cliff at the end.
Pan’s Labyrinth pulls exactly the same stunt regarding the belief in magic changing the ending, but they actually set it up. Whether the magic in question is real or just a child’s imagination is an open question throughout the story, but we see enough of it to believe it could be real. So the question gets established early, built up, then paid off in the ending, even if not precisely with an answer. If a story sets up a ‘what you see is what you get’ world, springing an ambiguous ending on the reader is short-changing their time and trust.
I’ve read bits of an interview with the director of Pan’s Labyrinth in which he states that the magic is real, and gives points in the film that point to the reality.
In one of those tastes-really-do-differ, you-can’t-please-everybody moments, the author of the blog post where I read the interview waxes cranky at the director for not leaving the ending ambiguous.
Hm. Or perhaps not ambiguous enough? Whether there’s a right ending or not, though–he put that gun on the mantle-piece in the first act. It didn’t just appear out of thin air at the end.
The other thing about ambiguity and endings is that people often seem to get confused between making a point/artistic statement and giving themselves an ‘out’ because sad endings make people sad. Tragic endings don’t work if the creator doesn’t own them.