Weeds' season three closing episode "Go", where protagonist Nancy Botwin burns down her entire drug-dealing operation, felt like a series finale, not a season finale. But then the show just kept going. Escalating into ridiculous plots including one where Nancy breastfeeds her adult brother-in-law, the show never really recovered. Maybe Weeds should have just let the fire burn out.
On the Other Hand... The fourth season of Weeds is mixed, but it's not terrible, so I can see why people kept watching. There are a few good episodes in the later seasons, and creator Jenji Kohan knows how to pull off a jaw-dropping season finale. Plus, the third season finale doesn't provide closure that later episodes tied up.
#sixseasonsandamovie has long been the mantra of Community fans, and with six seasons in its rearview mirror, a movie may not be out of the question. Which would be fine if every season of Community was as good as the first three. The firing of Dan Harmon was the first big mistake, and after the exits of three main cast members, it became extremely difficult to maintain a status quo. Why did we try and demand so much more than the show could give?
On the Other Hand... With the return of Dan Harmon, season five was an excellent recovery, and even seasons four and six had outstanding episodes like "Cooperative Polygraphy" and "Modern Espionage" along the way. The series finale ended up being fantastic, so even if the road to get there was a bit bumpy, in a way, it was all worth it.
Futurama's season four finale had everything: Jokes! Musical numbers! Heart! Memes! You really couldn't ask for anything better to close out an outstanding show. But then Futurama continued in the form of four mildly disappointing TV movies, followed by three seasons of mixed results. It's not that these seasons are bad per say, it's just that the season four finale is just so perfect that it kinda undermines everything that came after.
On the Other Hand... Seasons six through nine are actually pretty good, truth be told. Unlike Community, the out-of-show production issues never decreased the quality of the program, and the series finale "Meanwhile" came quite close to matching the amazingness that is "The Devil's Hands Are Idle Playthings."
This one's a bit tougher to mark exactly where the decline in quality began. Around season two or three, the show suddenly went from a bloody fun romp in vampireland to a "serious" show with "serious" characters and "serious" mythology. But you really can't make a show "serious" once basically all of its characters have engaged in a giant mythical orgy. It just doesn't work.
On the Other Hand... The season finales never really wrapped everything up, so it's hard to stop watching with no closure. Season five was also a solid resurgence with a compelling vampire bible plot and a great villain. And season six had its moments, I guess.
One of the greatest sinners on this list, Dexter took an extremely strong premise and a talented cast and drove it into the ground after two seasons.The main problem? The writers kept Dexter from facing any real consequences, even as he continued to literally kill people on a regular basis. Dexter probably would have been better if someone had slit the show's throat before things went south.
On the Other Hand... The Trinity Killer in the fourth season is actually an impressive Big Bad who rivals Dexter and keeps the momentum of the season going. The beginning of the seventh season is also a high watermark in the later seasons.