I think that I am the only Lost fan in the world, and by that I mean of who I know and from what I have done reading of on the internet, that liked the first six episodes of the third season. Sue me!, but I thought that they were a great little mini series...
... And that's in proper hindsight, too!, given that I have seen season 3 twice.
I've seen season 1 through about twice and then random episodes a few times more, and it held up. Though it really does feel like the first season of another show at times.
I watched season 2 through twice, once at US pace and then again when it was on over here. I found the second time through almost unbearable, and I'm in absolutely no hurry (the odd episode asside... Actually, a number of episodes asside, to give it its due) to watch it again. It was, generally, a mess and the worst season to have on when people are trotting out the tired old reasons that they don't watch Lost anymore.... Because the season plays up to them to the letter!
Season 3 I really enjoyed.
Season 4 I've only seen through once, and I've only just realised that. Maybe my episode recap starts there and starts tonight! Must... Resist... Urge to... Skip to... The... Constant.
(Sorry!, I've got to go with public opinion there, best episode ever?)
I did like season 5, but can't help but feeling that it would hold up a lot better under a DVD session over a few days. I felt let down by huge swathes of it, most notably the supposed Richard centric episode, but as I said at the time, I guess that a lot of that is down to the previews and synopsis that were released... The yanks are insane when it comes to that kind of thing though, anything more than a glimpse of parts of the first ten minutes of an episode are tantamount to spoiler in my eyes, and yet over there they are pretty much willing to use parts of the last scene in their, err, sneak peaks... But some of the synopsis were just down right misleading!
Oh, and on the edit, though they were treading water for a bit in the finale the final scenes were the best of the series!