The problem with Lost was that early on they created this amazing world, but there was never any planned story to tell. Lindelof kept promising everyone that it was all under control and they were following some grand plan. Until the last season...which was basically an "oops, we have to end this and have no ****ing clue how to."
I saw an interview with Lindelof where he went on about ambiguity and its importance in story telling. And I do think ambiguity can work (see: inception). But it can't be used as a crutch to wipe away all the story telling you've done because you never had an answer in the first place.