The Office. I'd argue the overwhelming majority of the first three seasons are amazing episodes (like 95% of them). Then the show declines over the next two seasons and for the next couple of seasons it is downright cringy at times. You have a few good episodes scattered about but for the most part, whenever I go back and watch the show in the later seasons I skip over chunks of episodes to get to the next good one.

Off the top of my head, I'd say that the episode where the Sales Department wants to get their hands on the new leads that Michael got from corporate is the episode that showed the writers ran out of ideas. They didn't know what to write about so they completely changed the behaviors of most of the sales people to fit the story they came up with. Jim is normally a pretty nice and level headed guy (aside from with Dwight) and in this episode all he's arrogant and doesn't care about anyone outside of the sales department. Phyllis is usually very timid but she turns into this cocky woman out of no where. I think even stanley, who normally has the attitude of "I'll do the bare minimum amount of work that lets me keep my job" goes all out to get the leads.

I personally would have been happy (in hindsight) if they ended the show at the season 3 finale when Jim sticks his head into the interview of pam in the conference room and he asks her out. The biggest story line of the first three seasons is resolved and they don't have to make up these fake problems that Jim and Pam begin to have. I also think it is just better to end that story line in a slightly ambiguous way. All he does is ask her out. If the show ended there, you wouldn't know if their relationship is successful but you could go either way with it sort of like the end of Inception.

Last thing I'll say is that I think they had another organic chance to end the show right after Jim and Pam's wedding. The characters were a bit different at that point but that is the "Happily Ever After Ending". You can assume, since it's a happy story, that Jim and Pam do stay together forever. The last scene is basically a celebration of the entire show so far. And even more of the episodes after this are grasping at straws.

So yeah, I think the office might have jumped the shark twice.