The first season, which is supposed to be the only good one, is profoundly tedious. Starting with the second season, which everyone hates, the show becomes rather wonderful. Suddenly all the grasping, both in terms of mythology and storyline and in terms of the show's essential focus, is gone, and it turns into Myst: The Series.
The problem with season one is that it makes the unfortunate assumption that the audience should identify with the characters. Considering that they're all pretty shallow, narrow-minded, and a little bit insane, this makes for some painful viewing. After season one, they realized it's more interesting to take an objective distance. Yes, these people are all nuts -- and they're all part of the puzzle. so let's sit back and watch them like lab rats, instead of trying to empathize with them.
Also it's clear that between seasons they sketched out a rough idea of what was actually going on with the island, as with season two suddenly the show has momentum. You'll recall that it took an entire season just for Locke to open the frickin' hatch. Practically nothing happens in season one, except that they see a few Others, and a polar bear, and the smoke creature (was it even depicted in season one, or was it just trees and noises?). Then each subsequent season is, by comparison, hugely compressed in the time it covers, yet is chock full of event. And most of it is relevant!
Speaking of pace, despite what everyone who loves season one says, from almost the start of season two, the show has been pretty consistent in explaining itself as it goes along, at about the same rate that it points out there's something bigger going on here.
The show can't keep up its steam much longer. Still, there are only, what, thirteen episodes left.
I'll agree that it's very much an NP series. Those who expect answers or straightforward explanations are going to go a bit batty. Those who want a constant stream of semi-epiphany, as an amorphous shape warps and grows more distinct, this is about as good a plaything as any.
The show works much better on DVD than on TV. On DVD, the episodes just flow into each other like chapters in a book.