Arrested Development
Arrested Development is one of the best written comedies in the past 20 years. Unfortunately, I believe it was a little ahead of its time. This show had three original seasons of some of the driest humor, yet funniest moments you'll ever see. The show even gets better with age. Despite AD's incredible star ratings, it struggled on tv. After three seasons, it was cancelled. Years after the original show was cancelled, Netflix rebooted the show. And it was a mistake. Michael, the only character previously who had his life and priorities in order, now has his life in shambles. All other characters lost the humor they once had and the only thing the 4th season has is the same inside jokes from the previous seasons.
Community
For those who have watched the show, you know how hilariously absurd it can be. In the first three seasons, the show is incredibly well written as we laugh the whole time through all the impossible shenanigans these characters get themselves into. Childish Gambino plays a goofy jock turned possible plumber while we have Chevy Chase make another TV appearance as the crazy old racist, Pierce. What could go wrong? Well, the show just kept going even after the jokes were all dried up. Even season three is stretching it a bit, but season four and on is where you can't get through a full episode. Seriously, from season 4 on you have to be either looking on your phone the whole time or switching it to something you've already seen 10 times (for me this is the office). As season 4 flopped, season 5 is where characters slowly leave the show. Their replacements never fit the bill, yet the show went on for a 6th season. Just stick with seasons 1-3.
Lost
Come on, this one is obvious. Right? The first season was some of the most suspenseful and dramatic TV around. If you haven't seen it, watch the first season. After that, it slowly digressed. You have a killer smoke cloud, an island polar bear, and no central antagonist. That "antagonist" title goes from one entity to the next and it's still somewhat unclear who the real opposing character here was.... For long stretches of time in the series, nothing would happen. Episodes are over 40 minutes long and throughout later seasons, they go through about only 3 minutes of real change and action. It will bore you to death. Tragically, this show continued to "try" to have a plot for 6 seasons.
Agree with my list? What are some other shows that went on for too long? Disagree with any of my picks? Let me know!