Actually, I found the season's ending a bit contrived and ragged - particularly the old tired act of the villain (Keamy) coming back from the dead so he could be killed off one more time. Death seems to be a temporary thing on this island anyway, sort of like in cartoons.
If Ben says they all must come back to the island, doesn't that include Desmond? And if not, why not? And if Ben destroyed his "way-back machine", how is he able to keep showing up in other parts of the world?
I'm not sure how they can twist the remaining plot lines for three more seasons without making a totally mockery of themselves.