Woohoo

I can't really think of the shows I watched a lot... But CN shows suffered from this sometimes. I thought Johnny Bravo got a lot worse after they fired Van Partible, for example (I know some people think the opposite, but I thought the early episodes were a lot funnier and better designed).

One of the shows I watched recently, "The Twisted Tales of Felix the Cat" is also thought to have lost its quality in season 2 (a lot of creative differences, executive meddling and such). I definitely found it weaker than season 1 (more inconsistent in quality, voice changes, one annoying character addition), but not really bad – I'd rank the best episodes about the same as in season 1, but there were definitely some forgettable episodes.

-MLP:FIM after Season 5 (S7 was an improvement but dropped the ball again with S8-9.)

-Hey Arnold after Season 3 (Not a huge decline, but pretty noticeable.)

-Family Guy after Season 5 (S6-8 had its bright spots, but nowhere near the caliber of S1-5.)

-Fairly Odd Parents after Season 5 (The less said, the better.)

@Woohoo 

Yes, season 7 felt like FiM was getting back to what I liked about the show and then the eighth and ninth seasons felt totally different, IMO.

The fourth season of the 2012 Teenage Mutant Ninja Turtles Nickelodeon cartoon where they went to space when I stopped watching the show.