I finished Dostoevsky's Notes from Underground recently. It was good, as all of Dostoevsky's books are, but it was also a downer. Spending 130 pages inside the mind of a sick, wicked man is mildly depressing.
Whenever I finish one of Dostoevsky's books, I involuntarily ask myself if it was worth it. They are always well-written, compelling, and deeply Christian. But they are also invariably dark. I'm not sure whether the former qualities justify the latter.
I would love to think they do. Dostoevsky is one of my favorite authors, and the darkness always has a purpose in his novels. Sometimes it is redeemed or overcome in the end (as in The Brothers Karamazov and Crime and Punishment), and Dostoevsky is also good at writing hope and redemption. But usually you have to make it through a clear look at deep, deep depravity to get there.
Dostoevsky is fantastically good (too good?) at writing evil convincingly. I think I'm afraid that I enjoy being drawn into the dark worlds he creates a little too much. What do you think? What amount of darkness is it healthy for our souls to digest? Is it ok as long as it serves a larger point? As long as it is redeemed?
 Dostoevsky, by the way, was aware of the problem that writing evil well is so much easier than writing good. The Idiot is his attempt to over come this by writing a wholly good character.