Lost is on the decline. We'll see how season 3 goes but season 2 was a definite letdown when compared to season 2.
24 had one of its weakest, yet most critically acclaimed (and awarded) seasons last year. I'm not very optimistic that it will ever be as good as the 1st few season. I think its a limitation with the premise. You can only do so much with 24 realtime episodes a season without it getting to a level of absurdness.
Prison Break season 1 was perhaps one of the greatest single seasons of TV I can ever remember. Unfortunately, like 24, given the constraints of the storyline, it will eventually run out of steam despite season 2 not being too bad so far. Its really too bad because I love seeing shows that do something so creatively different than everything else out on TV.
I'm kind of disappointed The Shield isn't in the poll. That show, despite ups and downs, never fails to disappoint. If it was on network it would be much more popular than it is already. Unfortunately, if it was on network TV, they couldn't make it as gritty and real, which is definetly its greatest appeal. The term "shades of gray" applies to just about all the character in this show and I can never get over how interesting they manage to make the storylines. Its one of the few shows that is both equally character driven and story driven, with both of them done very well.