I think down the shitter is a little strong, but I don't disagree that the show definitely had some logistical problems that hurt it a fair amount. That first season was just dizzyingly good is probably the bigger part of the problem. These are the same guys who did 24, which I didn't watch after like season 2 or 3, I can't even remember, but that had a similar problem. They're sort of out to get the most tense thing they can get, and if it paints them into a corner as it often seems to do, they'll just try to write themselves out of it over the next few episodes, and they're sort of asking the audience to bear with them. It's just that as time wears on the corners they paint themselves into just get more and more.
Still an excellent show.
I read an excellent theory once that the show got off the tracks in part because Brody was so good in season one, and won an Emmy for Best Actor, and the whole deal, that they may have wanted to go in a different direction with the show, perhaps even have him die in that bunker, but just couldn't.
The show is shot really late vs. when it airs than almost any other show. And it's something of a known commodity that this group actually reads and listens to what their audience says. They even admit to it, as opposed to most showrunners who claim to not read message boards or listen to reviews or the like.