It might be too early yet, but here's my review of the seasons and what each one means to me.
Season 1 - The one that started it all and created the fandom. It set the initial pace and atmosphere of the series, and many classic episodes, and moments that became memes. It introduced us to these lovable, relatable, adorable ponies and gave us pretty fun scenes with them.
Season 2 - Now that the writers know about the fandom, they stepped up a bit, giving us an actual villain in the form of Discord who is more fun to have around than Pinkie Pie (and she's still funny at this point). There are several episodes I thought were good, and they're more fun than a lot of the Season 1 episodes. Ending with the show's unexpected first Knight of Cerebus and truly epic episode.
Season 3 - Not very popular, some episodes were dull, but the episodes I liked, I thought were awesome. The Crystal Empire, for having an even darker villain and destroying him up front; Magic Duel, for Trixie's return and the way Twilight tricks her into removing the amulet; Sleepless in Ponyville and Wonderbolts Academy both for showing the better side of Rainbow Dash's character that a lot of fans can't see; Keep Calm and Flutter On for Discord's return and redemption; and Magical Mystery Cure, for being a musical, and Twilight becoming a princess and alicorn (which got a lot of hate, but those still in the fandom accept it now)
Season 4 - Had the most awesome episodes IMO, including my favorite episode: The unrivalled epic Twilight's Kingdom, also featuring the G4 reboot of the first ever My Little Pony villain back in G1. Though it also has my least favorite episode.
Season 5 - Doesn't have as many good episodes as Season 4, but has some of the most sensational episodes of the series: Slice of Life, for all the stuff thrown in for the fans; Do Princesses Dream of Magic Sheep, for similar reasons mixed with epicness; The Cutie Remark, for the alternate futures of the previous villains; and, above all, Crusaders of the Lost Mark, where the CMC finally get their cutie marks! Episodes that also count for something are Tanks for the Memories (for Rainbow Dash having her first song), Amending Fences (for going all the way back to Moondancer from Episode 1), and Rarity Investigates (for being a long-awaited Rainbow Dash/Rarity episode). This makes Season 5 my favorite Season.
Season 6 - Not quite as good, but it did have some pretty fun episodes, such as Gauntlet of Fire, A Hearth's Warming Tail, The Saddle Row Review, Spice Up Your Life, Stranger Than Fan Fiction, Buckball Season, and To Where and Back Again. Even though it did two things I feared it would, I can accept them now.
Season 7 - Not as many great episodes, and took 10 episodes to get an awesome one. I'll have more to say as the season progresses.
Ranking for the seasons:
- Season 5
- Season 4
- Season 2
- Season 3
- Season 1
- Season 6
- Season 7