I don't really see anyway that they can have a resolution that can satisfy, as time goes on expectations have been built too high. Plus, it seems that we have analyzed so much and thought of every possible scenario that nothing could be a surprise, unless it was totally absurd. I'd be happy with a conclusion where the characters reach some kind of catharsis and are content with their current state and situation and have that be the ending. it's not important to know all of the answers because it will never be enough.
Disapointing, sure. But look at the past season and ask yourself if any of the scenarios popping into your head gave you a clear answer as to who is in the coffin. Why are they going back to the island? Who, what, where, when or why.. and HOW is the island ANYWAY?
If we cant see the plot twists, then we cant see the end. It hasnt been predictable so far, so.. at least I dont see how the ending can be anything less than spectacular.. paranormal.. twisting all over the story-trail but still feels like we're being lead somewhere.
On the optimistic side of things.. it cant be worse than the endings to X-Files or Deadwood. Insult + Injury = X Files: I want to bereave.
Huge buildup + Cancelled series = Deadwood: I want to.. oh wait, the bad guy won and America is built. That's too close to reality.