Decent, but nothing to write home about.
Pretty good for a kids show, but nothing special otherwise. Starting off, it takes no real risks with the characters. The tomboy having self-worth issues, the shy one having a hidden strength, the bookworm and "straight man" so to speak being not so above everything after all, the seemingly high-class one actually being sweet, none of that is new. It's all been done before and frankly, all been done better.
The Aesop's are often subject to Fridge Logic
and Unfortunate Implications
, with Mysterious Mare-Do-Well, Dragon Quest and A Friend In Deed being three of the most prominent examples. There have been entire headscratcher, wall banger and dethroning moment pages on those, so I won't go into them further here.
The world-building is lacking to say the least. Despite seeing griffons, minotaurs, zebras and dragons, we know almost nothing about any of them (other than dragons being jerks every time they're seen). Plot elements often come out of nowhere despite opportunities to set them up earlier, such as Shining Armor. This is likely in part due to the episodic nature of the show, but it's still jarring.
One would expect a largely slice of life series to not have many overarching plotlines, and one would be correct. Powerful threats like Discord, Sombra and Chrysalis are brought up and then dealt with in two episodes at absolute maximum. There isn't much build-up, nor are we given much insight into them. Where they come from, how they came to be the way they are, any sort of insight into their characters simply isn't there.
This ability to take down seemingly epic threats easily and then spend a whole episode trying to figure out who ate a cake or an entire episode not realizing they have the wrong person can also jar a more serious watcher and threaten to break the suspension of disbelief.
Now, I've been pretty negative here, so let's get on to what the show does right. The animation is fluid and easy to watch. The songs (with a couple of exceptions) tend to be well-written and enjoyable, and it does manage to work the aesops in without being irritating.
As a childrens show, it is a good, though not spectacular series. However, it fails to build the world, tell any sort of continuous, compelling story over the seasons, or go very deep into anything, and generally lacks to substance to be anything more than a good kids show