A lot of people seem to hate Season Six. It's not as good as the older episodes. They're messing up the value of alicorns. All that crap.
So, let's actually sit down and take a look at when MLP jumped the shark.
wait what the heck does that mean
"Jumping the shark", according to Wikipedia, means, "an idiom popularized by Jon Hein that was used to describe the moment in the evolution of a television show when it begins a decline in quality, signaled by a particular scene, episode, or aspect of a show in which the writers use some type of gimmick in an attempt to keep viewers' interest, which is taken as a sign of desperation, and is seen by viewers to be the point at which the show strayed irretrievably from its original formula." Basically, the show does something so outlandish or desperate that the show starts to degrade in quality. This comes from the show Happy Days where a main character literally jumps a shark on water skis. Seriously.
case 1: it's all a conspiracy
Maybe MLP:FIM actually sucks. Maybe Lauren Faust was only in it to get people to want to love it because it's Lauren Faust. Maybe this is all a plot by Hasbro to make as many people as possible buy toys, so they get the best people in the business to make a good show to get people to buy toys. Hasbro has won. They can do whatever they want with the show, but every brony still wants the show to be awesome. People still buy toys. People still buy merch. Because Hasbro has won the mind game. Take a red pill guys. Spread the word. Let the tru-*dies*
Yeah, it's silly, but it could be a possibility.
case 2: when Lauren left the show
This isn't really a case of "jumping the shark", but it could be a point where the show started to suck. Of course! Lauren Faust left! Our lord and savior left the show, so the show became crap!
Though, some say that it's good that Lauren left the show, because then the show could cover more topics in more different and complex ways than Lauren did. What do you think?
case 3: when Twee-lee Sparkle-Corn became a princess
This is classic jump-the-shark material. "LOOK GUYS! THE MAIN CHARACTER BECAME A PRINCESS!!! BUY OUR TOYS!!!" Many bronies complained about this when it first aired. There was even a petition to change the canon back. This so far makes the most sense as a "jumping the shark" moment.
case 4: when Twilight fought Tirek in the Season 4 finale
That fight scene was awesome, wasn't it? It seemed more like a Dragonball Z scene than a MLP scene! Yet, maybe that scene was too great. The staff made something so good, so great, that they possibly can't make anything better than that. Plus, with the blatant market-ism of Twi's new castle, they already went downhill in the same episode! Jump-the-shark material maybe?
case 5: when Starlight Glimmer was redeemed
It could have been done better. Why does everypony all of a sudden forgive Starlight? She did some pretty messed up things! You can't just do a complete 180 and expect everyone to accept you for what you are now. Yet, that's exactly what happened. "Friendship", right? Everything is not rainbows and sunshine. If you make mistakes, you have to live with them. Everyone involved will too, and it will take a long time to make up for that. The Season 5 finale completely jumped over that fact and basically said, "Even if you did terrible things, everyone will immediately love you if you stop doing it!" No. That's not how life works.
case 5.5: the whole of Slice of Life
"Hey guys, we know that bronies exist! Let's make an episode about the background characters and put a bunch of memes in it! Everypony loves that!"
case 6: maybe it's just us
Maybe we're all just a bunch of nitpicks, criticizing every single thing about the show because we had our own dreams of where it would go, and now they're ruined. You have to understand, the people working on this are human too. They have their own visions, and just because they're not what you have doesn't mean you have every right to bash them. If it's a good episode but not what you expected, don't bash them just because it wasn't what you wanted. Look at the episode by itself and compared to the episodes from the rest of the season. This show has evolved over the years. You have to accept that. I'm not saying though you can't criticize an episode. I'm just saying that criticizing it just because it's not what you wanted the show to go is self-centered and makes you look like what all the anti-bronies think you are.

Thanks for reading. I'll make this into a video soon, but for right now, here's a blooge. See ya.