As Lost enters its final season, it's become clear that there is no better show on network TV (not that I watch basically any other network TV, so how would I know...) Although the final season is structured quite differently from all those that have come before it, it's still turning out to be an enthralling apex for the show to go out on, for at least three reasons:
First, it's ambitious as hell. The whole show has basically become an extended discussion of the concept and nature of fate, free will and causation. It's had a sideline into time travel, and alternate universes, and that sideline is still going, and somehow the show still works! There has never once been a character on the show whose motives weren't ultimately clear and understandable, and yet at the same time, basically every character appears to be driven by motives that, until they're explained, are a total mystery. I have no idea how they manage to strike this seemingly insane balance.
Second, the fundamental mystery that drives the show remains satisfyingly unanswered. Think about it: what's the deal with the island? At the heart of the show, this question above all others remains unanswered. The two demigods, the lighthouse, the cave, the temple...all the recent additions to the mythology of the island have explained a ton, but at the same time left the basic question unanswered.
Third, each week is just a solid hour of gripping television. All of the above would be beside the point if each episode weren't packed with action, intrigue, mystery, good writing, solid acting, beautiful (if workmanlike) cinematography, and just pure fun. It's just a fun fucking 45 minutes, every episode, and that makes the whole magilla work.