Sarah Langan's The Keeper is a horror novel that doesn't quite succeed, and I'm musing about why. Part of the problem, I think, is that you can tell from early on which characters she likes, and you know that they'll come out of everything unscathed. Other writers have the good and bad suffering alike.
But it's not quite so simple -- I loved Heart-Shaped Box, and I think there's never any doubt that the protagonist will prevail, and it's pretty unlikely that his girlfriend will die. I think the difference is that Joe Hill performs some narrative sleight-of-hand to keep you from seeing it too closely -- Jude gets injured pretty severely, and his employee dies right near the beginning. Langan, on the other hand, really pushes it in your face, paradoxically by having more characters die. There's a section about 2/3 of the way through where about 10 characters die in horrible ways, but it's not scary because they're mostly ad hoc characters -- they don't really exist outside of that chapter, so it's hard to care what happens to them. More importantly, it drives home the fact that Langan doesn't want to take out any characters that she's spent any time on developing.
I'm in the middle of listening to Tennyson's Idylls of the King, so I don't have a complete opinion of it, but I wanted to note something that I like. It's mostly the story of various of Arthur's knights, and Arthur doesn't feature heavily in most of the stories so far. This gives Tennyson a chance to mention Guinevere's affair with Lancelot in passing in the stories, so that we get a sense of how long the affair is actually going on, and how pervasive it was (as various knights avoid thinking about it, or as Guinevere and Lancelot cover it up) . I think that versions which focus on the triangle never really give you that sense.