The original premise of the show was intriguing with a clear beginning and (possibly) end but as with all popular "limited" shows it was extended to last longer. It should get credit for it's will to write off unnecessary characters along the way, but a laughable conspiracy plot (what else) and overdramatic plot twists soon made it into a parody. The ending was a spit in the face until the revival changed it.
Although season 3 is a bit of a guilty pleasure for me (I heard it's hated), I think this thing should have ended right after the first season, i.e. while it was still kinda good. Everything after it is pretty much pointless, full of just laugh-out-loud kinds of inconsistencies and resurrections, especially the WTF-moments-filled last season.