Libby's story is "pretty much finished?" They've been teasing us with her backstory ever since she was killed off in the second season. We still don't know what she was doing in the mental institution with Hurley, and there's also the matter of Desmond's sailboat. She's been in the backstory of two major characters with no explanation.

I was disappointed when they brought her back for Michael's flashback only to waste the character on a couple of throwaway "ghost" scenes, and now they tell us her story is finished? Didn't they, at one point, tell us that what we'd seen of her backstory was only the tip of the iceberg?

I think the biggest issue I had with season 2 was some awkward pacing and the fact that much of it turned out to be pointless due to all of the deaths. Anna Lucia I can deal with and I'll even buy that she was always meant to die. Ecko's death bothered me because it seemed like they never really tapped into the the character's true potential and just couldn't think of where to go with his story. But at least we were shown his background and where he came from.

Libby, on the other hand, just pissed me off. They clearly had a back story for her and we just never got to see it. She just strikes me as the quintessential loose end. Ultimately I don't think her story matters much in the overall scheme of things and that's why we'll never see it, but I think many will agree that the reveal at the end of DAVE, especially the look on her face when she walks away from the cliff with Hurley, was a really cool moment. No resolution to that moment makes it meaningless and kind of annoying on repeat viewings.

Just for the record, I doubt we'll see any kind of satisfactory backstory/explanation for either Rousseau or Walt, no matter what the writers say.