I haven't read the original books of Tolkiens', except for the Hobbit, which I practically inhaled when I was ten (I read a lot for my age, notably books like Jurassic Park and Carrie before I hit middle school), so I'm not sure what 'original ending' you refer to concerning Frodo and the others. I'm gonna go raid my sisters' library in a bit.

Whenever I write stories, so often they end ... 'weird', as someone once described them to me. Even if they're happy, they're bittersweet. I don't like 'dancing away into the sunset' type endings, because they feel false, like there wasn't a big enough sacrifice going on. RoTK's strength, I felt, was that Frodo still sort've lost. Sure, he destroyed the One Ring, but his scars never healed, and he never felt at home again in the Shire. You can see it in his face, even a few years later, and then off he goes to the distant shores with Gandalf and Bilbo and the elves. It's like all the magic leaving the world. I was pretty sad about the elves' leaving.

Fight Club's original ending by Chuck Palachniuk was different than the movie version's (although I prefer the latter's), but no less dark. Lolita, Wicked, Requiem for a Dream ... Titus is in particular dark and bizarre.