I don't like films with bad endings like Open Water (yeah, I know, it's based on a real event, I read the news). What's the point of wasting two hours on a struggle that ends bad? There's no payoff and certainly the path isn't the goal in a film where the path is extremely unpleasant.
An unhappy ending is as valid as a happy one, and often fits the story more. I'd kill to see the original ending of The Magnificent Ambersons