As with every show, Lost had its ups and downs. But which season had the most downs?
I don't like season two or four. I'm not sure why on season two, it just felt weird in places. Season 4 because it derailed into time travel terrority and just got a little too much for itself in places imo. It got back on track in five though.
Either Season 4 or 6. I watched both seasons faithfully, but I don't find them easy to rewatch.
I did not care for Season 4's central plot lines, which were Widmore's attempt to usurp Ben and the Oceanic Six leaving the Island. Since Jacob had already been strongly alluded to in Season 3, I never bought that Ben and Widmore were the great masterminds that the writers wanted us to think they were. Their feud was rather petty, as neither was better than the other (although we were supposed to be more sympathetic to Ben). As for the Losties, the Season 3 finale had already made it abundantly clear that they were not supposed to leave the Island; it was like an accident waiting to happen. Granted, their leaving was necessary to raise the stakes in later seasons, but it wasn't very interesting to watch; the Jeremy Bentham mystery shouldn't have been drawn out, either. Finally, the season also suffered due to the 2008 writers' strike, but that's an unfair complaint.
Season 6 failed to meet many people's expectations, especially fans like me whose main interest in the show lies in its many mysteries. Most of the answers given in this series were not satisfying and reflected badly on previous seasons. The character motivations were also rather iffy, as most of them were just running around the Island without having a clear plan. Why did no one set out to understand what danger the Man In Black posed to the outside world? They didn't trust him, but they weren't quite as afraid as they should have been, either. Perhaps the problem was that they seemed to view him as Locke more often than not. The Flashsideways were nice in the finale, but otherwise they were just a misdirection; the time could have been better spent on fleshing out the Island story. For the record, I was never in favor of the idea of rewriting the timeline (nor did I think it would happen), but I think the afterlife should have been addressed in the finale only.