)
For me, many of the show's attempts at worldbuilding were so half-hearted compared to fan ones that I can't help but wonder if they would have been better off leaving them alone. (I call this the Griffonstone Effect.)
My opinions of seasons tend to be pretty fixed - might tie in with my lack of rewatching. (Sonic Rainboom I actually found a relatively weaker episode at the time - Rarity's performance really seems OOC.)
And I think that some plots are naturally suited for different parts of the show - you couldn't do Forever Filly in Season 1 or even 2, and you couldn't really do Dragonshy or the first part of Griffon the Brush Off in Season 4+. (Some later plots do feel like they should have come earlier - sometimes it works anyway and other times it doesn't.)
And the art quality certainly improved... but the show looked pretty good from the beginning. (One thing I *don't* miss is background clones, though.)