After seven seasons, I can't really say that MLP has gone in any one particular direction. It's more certain trends of seasons that stick out to me, but while I might remember an episode, I'd have a harder time placing it.
But I guess I can say:
-Season 1: Decent, very much a pilot season of sorts. Has a charm, but often gets too cutsie. It's FiM before it really took off, and the creators realized it had an adult fanbase as well.
-Season 2: A huge step up. I feel the show really hit its stride here, as while it didn't abandon its tone, it did make allowances for more mature viewers, which led to villains like Discord and Chrysalis, and far more 'wacky' episodes.
-Season 3: The point where it started to falter for me, for a variety of reasons. We start with the worst villain the series has given us (Sombra...and yes, I know the comics flesh him out), and ends with Twilight getting wings that feels like a desparate attempt (within the episode) to say "see, we planned this all along! How dare you suggest that we needed to sell a winged Twilight toy, forcing us to pull out an explanation from the blue?". Looking at the list on Wikipedia, there's also nothing that really stands out for me either - maybe Too Many Pinkie Pies, but apart from that, and the season openers/closers (for the wrong reasons), that's about it.
-Season 4: Season 4 is a step up from 3, and reminds me of Season 2 in a few ways. It's also at this point that I feel the series really started to benefit from string continuity. If Season 1-3 is the roadmap of Twilight getting to be the Princess of Friendship, Season 4 is her coming to terms with said role. It also introduces the more wacky episodes that I missed, with stuff like Pinkie Pride, Power Ponies, Daring Don't, etc. That, and also Discord's arc...sort of. And while Tirek is a 2D villain, he's at least an entertaining one that has balls to the walls action, with actual gravitas (Twilight loses her library). One downgrade I think is trading in the Elements of Harmony for the rainbow...stripe...things (God, I can't even remember what they're called). Like Twilight's castle, it felt like another excuse to sell toys, but unlike Twilight's castle, felt less in sync with the plot.
-Season 5: Overall, I'd call this a step up from Season 4, as it employs its strengths (string continuity, via the magic map), introduces Starlight Glimmer (who in this season, is a good addition), and gives us episodes like Lost Treasure of Griffinstone, Slice of Life, Crusaders of the Lost Mark, and Rarity Investigates. It also has a good ending...mostly. I mean, I can't feel sorry for Starlight Glimmer, but she at least presents herself as a good antagonist in this season. At the time, I remember on this forum that someone said that season 5 felt like an overall conclusion, and I could see what they were getting at. The Crusaders finally got their cutie marks, and Twilight appeared to have come full circle, starting off as a student, and making her way up to the point where she could take on a student of her own. Which brings us to...
-Season 6: A step down from Season 5 for me, and I think possibly the weakest season since Season 3. Thing is, Season 5 introduces a great concept, Twilight stepping into the role as teacher, and Starlight getting the spotlight. Thing is, this isn't what happens. Starlight comes in from time to time, but in what really should have been her season IMO, it's more business as usual. Likewise, while the previous seasons benefitted a lot from string continuity, this one doesn't employ it nearly as memorably. I mean, for instance, the Crusaders now know what to do with their marks, but it's less compelling than seeing them strive to get them. Rainbow's in the Wonderbolts, Rarity's doing well business-wise, Fluttershy has become more confident...with the Mane 6 having mostly achieved their goals, or in places where they were happy in life from the start (Applejack, Pinkie Pie), I found the series lost a lot of its 'oomph.' There were some stand-outs, such as Starlight becoming friends with Trixie, and "Stranger Than Fanfiction," but we still had to deal with episodes like "28 Pranks Later." Oh, and the ending. Screw the ending. Damn the point where the series reaches such smultz that the entire race of Changelings becomes good because friendship is so wonderful and SPARE ME! Starlight completes her 'arc,' but her appearances have been so inconsistent that it feels hollow.
-Season 7: I'm behind on episodes, but so far it's a step up. I actually like Starlight now, and we've got some good episodes like 'Rock Solid Friendship', and 'A Royal Problem' (if only for seeing Daybreaker). On the other hand, there doesn't seem to be any overall direction for the season yet, whereas seasons 4-6 felt like they had an overall drive to get somewhere.
So, overall, if I had to rank seasons, it would be 2>5>4>1>3/6 So, in short, I can't say that the series has gone in any one direction quality-wise, as it's gone up and down for me. But I think the main issue is that it's lost a lot of its punch. Still enjoyable, but as the saying goes, familiarity breeds contempt.
