Unbreakable is one of my all-time favourite movies; I think it's fabulous. I particularly admire the way it captures the very gloominess you cite - not dark and dramatic angst, but just the way life quietly and bleakly seems to lose its magic. When the son makes his parents hold hands, and then their hands come apart as soon as he's not looking, that gesture speaks more eloquently about the state of their relationship than any drawn-out expository conversation could have. One of my favourite details is the way that David asks his wife if she can ever remember him being sick: his own life has become such a gray haze that he assumes she will know it better than he does.