Weeds may be the weirdest show on this list (or...any list). The basic premise of the show - skewering suburban life through the eyes of widow Nancy Botwin, a regular single mom who just happened to be a major drug dealer - was solid and flexible that it could have lasted a full run of 5 or 6 seasons without much fuss. And it seemed like that would be the case...until the season 3 finale, which saw Nancy basically burning the town of Agrestic to the ground, abandoning a good chunk of the main characters, and hitting the road to parts unknown. And that's where everything fell apart.
The show was great at doing shocking things and pushing its characters and premise to the very edge, but they pushed a little too hard with the destruction and abandonment of the show's setting. After that, the show grew increasingly ridiculous and unbelievable and turned Nancy from an anti-hero doing what she had to for her family to a straight-up sociopath who was actively destroying her children's lives, except all played for comedy, and following no logical arc. They go from a beach community to living with a cartel kingpin to on the run to a million other locales, none of which were as interesting or dynamic as the simple suburb the show started in.
Seasons Worth Watching: 1-3
2. Sons of Anarchy
Oof. THIS show. So good for two seasons, so Not That Good But I Kept Hoping It Would Regain That Goodness in every other season. Was it losing Half-Sack that killed it? Was it all the Ireland stuff? Was it giving Kurt Sutter so much creative freedom that every episode was like 90 minutes long and there were like 5 montages per episode? Why did Juice live that long? I don't know. I'll never know.
Seasons Worth Watching: 1-2 (there are two solid murders at the end of season 3 that are pretty great, though)
Dexter is sorta the poster child for shows going from critically and commercially popular and then suddenly coming to a screeching halt and everyone unanimously agreeing that the show is unwatchably bad. Dexter was always a PRETTY good show with some weak-ish elements (such as: Dexter's Ghost Dad, Angel's stupid voice, the increasing ridiculousness of no one in Miami PD recognizing Dexter was very obviously a serial killer I mean COME ON), but it was able to deliver true greatness in season 4 with the arc of the Trinity Killer and one of the most gut-wrenching finales of any show up to that point.
And then....uh, season 5 arrived like a wet fart, with nothing even approaching the intensity of the Trinity Killer. Season 6 was the season with Colin Hanks and the most "duh" twist of all-time in the nature of Edward James Olmos' character, and it was at that point that the bad elements of Dexter had truly won out, and left nothing really worth salvaging.
The series went on, and had some brief moments where it looked like things might get watchable again, but then the series finale came and went, and sealed Dexter's fate as a worthless show post-season 4 forever. I'm sorry, but there is no forgiving ending the show on Lumberjack Dexter:
Seasons Worth Watching: 1-4 (although you can skip most of the Jimmy Smits season, and any scene heavily featuring Angel/LaGuerta)
Listen, I love 24 - and it's a mostly great show, even if you need to discount the fact that they occasionally have a mindnumbingly bad storyline (Teri's amnesia, Kim's cougar-trouble) given the INSANE challenge in the premise of a real-time show taking place over the course of 24 hours. That's a crazy difficult thing to accomplish, and the writers deserve all the credit in the world for managing to pull it off, like, 8 separate times WHILE still making it pretty watchable.
And then season 6 happened, and the show really never recovered from it. Granted, expectations were pretty huge post-season 5 (for which the show won the Best Drama Emmy, and was pretty easily its best season in a while), and the show just didn't have any tricks left in its sleeve, so ended up doing things that pushed the suspension of disbelief too far EVEN FOR 24. A nuke went off in LA in one of the first episodes, Jack is revealed to have a secret family who are all evil conspirators, something about a Rain Man-type guy who helped terrorists make drone-nukes...it's all kinda a blur. The point is, you should just pretend Jack got kidnapped and taken to China and died there.
Seasons Worth Watching: 1-5 (although you can obviously avoid any scene with Kim and Johnny Drama)
You know what - despite being exactly the show everyone joked it was, in terms of how predictable the flow of every episode was, it was well-written and funny and pretty entertaining (when you're watching a marathon on TBS on a Sunday afternoon, at least). It certainly wasn't reinventing the wheel, but it was a solid piece of procedural TV entertainment.
But House had done a dance around the potential romance of Hugh Laurie and the hospital administrator, Cuddy. And like all "will-they-won't-they" TV romances, it sucked ass when they finally got together, which they did for an entire season. The show had been on a downward slant up until that point, when the repetitiveness of the show started to overwhelm everything, but the House-Cuddy pairing is what finally broke it.
Seasons Worth Watching: 1-6 (and hey, House's Head/Wilson's Heart are genuinely great)
6. True Blood
In its first season, True Blood was weird and fun and campy and sexy in all the right ways - it was genuinely fun to watch! Seasons 2 and 3 started to show signs of problems cropping up - too many characters, too many weird tangents, too many, uh, fairies. Like, actual fairies? And werepanthers? And now Bill is the Vampire President?! And c'mon now why are you still a character, Tara?
Basically, if the show would have ended the moment after Russell ripping out the spine of a news anchor on live television, the show would have ended in the most fitting and perfect way possible.
Seasons Worth Watching: 1-3 (although the rest of the show is pretty good for hate-watching, if that's your thing)
Man, fuck the last season of Lost. While it had it's shaky moments up until that point, it had always been incredibly watchable and a super fun show to talk about and theorize about online. But season 6 dropped the ball in the most insane ways possible - half the season was spent in "flash-sideways" (which were later revealed to be Practice Heaven or something, where there are no consequences because everyone is already dead), and the rest of the season was spent with the characters battling Island Ghosts over Magic Cave Light or something like that, which is never adequately explained, and thus the stakes never really make any sense.
And yes I still cried during the finale, but that's because Sawyer and Juliet are great together, so sue me.
Seasons Worth Watching: 1-5 (although the long-awaited Richard ep in season 6 is top-notch)
I mean....obviously. C'mon. You know this.
Seasons Worth Watching: 1 (although skip the Sylar fight because Jesus Christ what the hell, we built up a whole season for THAT?!)
BONUS! Arrested Development
This is a weird one, so it's hard to really include it with the rest - it's a half-hour sitcom, and it's final season was filmed years after the show ended properly, and in a completely different fashion from the earlier episodes. And in short, it sucked. Maybe it was too much hype and anticipation, maybe it was the fact that the actors were almost never in the same room at the same time, or maybe it was just that the magic had worn off, but Arrested Development's 4th season is a mess. It's got a few great jokes (it IS still Arrested Development, after all), but the magic of the earlier seasons is completely gone, replaced by a byzantine narrative structure that will just leave you more confused than entertained.
Seasons Worth Watching: 1-3 (although the first Gob episode in season 4 is pretty solid)