Something I've noticed is, during season 1, the series was very relaxed. Character interactions felt genuine, and mostly everything was very low on the scale of "importance". In season 2, the writers were fully aware of the older demographic the show attracted, and became obsessed with catering to them almost exclusively. The fan pandering was duly noted by the fandom, however, and most fans felt the series lost its innocence as well as its genuineness, as did I. Not only had everything become tryhard and over-the-top, but they did a BAD job implementing these risky ideas as well.
After the show came back from hiatus, season 3 seemed like a return to form for the series. There was much less cringe-worthy nonsense, and character interactions didn't feel quite as forced. The animation quality got a bump, as it did in season 2 (the 2nd season's bump was really more in regard to new vector animations and facial expressions for the each of the characters, while season 3's concentrated more on diversifying the color palette, as well as smoothing out said animations). All this was great, of course, however, season 3 was only 13 episodes long, which led many to fear the series may have been on its way out.
To fill the large gap between season 3 and 4, Dhx (the studio behind MLP: FIM) created a new IP based on the MLP universe"Equestria Girls". It was clearly a marketing ploy by Hasbro in order to get their dwindling delicious loli demographic to buy more toys, since, in Equestria Girls all the main characters are transformed into high school girls (besides Spike ofc. He gets demoted to a dog lol), and lets be honest, what's more marketable to little girls than cute Barbie doll-esque characters they can dress up? So yeah, it was supposedly non-canonical to the main series, but that didn't stop bronies the world over from threatening to commit suicide. *rolls eyes*
Equestria Girls was pretty fucking shitty. Thankfully they VASTLY improved upon the 2 sequels which came out years later.
Anyway, season 4 finally came to fruition, and right off the bat from the first episode, you could tell they were kicking things up a notch. The main characters started going through meticulous introspection, questions afraid to be asked in previous seasons were laid out in full, and over all things just started to get legitimately.... Good. I was kinda shocked, because, honestly the main reason I attached myself to this show in the beginning was merely because the characters were cute, and MLP was the PERFECT thing to troll people with online. I never actually expected it to become a quality cartoon able to compete with favorites of mine, such as Animaniacs, Samurai Jack, PowerPuff Girls, etc. Season 4 did a wonderful job of taking what season 3 set out to do, fully realizing it, and then expanding on it even further. Animation quality was improved upon once again, adding intense volumetric lighting effects which resulted in many beautiful set pieces strewn across the season. It was a full 26 episodes long, and concluded in such a way that I couldn't even conceive there being any way they could possibly follow up to it without being a disappointment....
...then came Season 5...
What can I say, even? There's nothing... no words can do this masterpiece justice...
-sigh- I suppose I must say SOMETHING, considering the friggin essay I wrote above >.>;
Season 5 made me question reality; how something of such magnanimous quality could even EXIST on television braodcasting utterly perplexed me. It made season 4 look like a joke in comparison. The best way to put it, would probably be (and this is complete speculation on my part) that DHX was planning on this being the final season of the show and they wanted every single idea, all those magnificent pipe dreams they WISHED could have been implemented earlier on, to be incorporated into the fifth season. Not only did they reach for the stars (an act which all but destroyed their credibility in season 2) but they took hold of them and lifted themselves through the stratosphere to never before seen heights of literary and cinematographic mastery!
They went places in this season... that you wouldn't expect them to even go NEAR in this kind of cartoon. And I'm saying even after watching the season 4 finale (ergo the one with that Dragonball-esque sequence I linked afore).
Season 6 followed shortly after, and it succeeded in meeting my expectations in nearly every way imaginable. While it "met" my expectations, it did not quite "shatter" them as season 4 and 5 had done in the past. I believe season 6 is perhaps a slight improvement over 4 in overall quality. One of the least interesting characters of season 5 (Starlight Glimmer) was fleshed out in an extremely satisfying way. I would go as far as to say, Starlight was by far the most enjoyable character to watch in season 6. This season also managed to pull off "fluidity" extremely well.
During season 6, there was another Equestria Girls movie released, and Jesus Christ was it bad. I was flabbergasted at the HUGE decrease in quality from the last two movies.... it makes me a bit worried for the 2017 movie tbh...
For those who are not "in the know" about all things MLP, There have been 4 movies up till this point, but all of them are technically non-canon. Every movie out so far have taken place in an alternate dimension wherein the ponies transform into normal human beings. With the 2017 movie, there will be none of this nonsense. Supposedly it will be a full length feature film (2-ish hours), whereas the previous EQG movies were around 40 min - an hour.