I love the original My Little Pony cartoon series, but it had it flaws. As a cartoon designed to sell toys, it had it's share of poorly-written episodes, pointless silliness, and careless animation errors. But it wasn't all bad, and it's poor reputation for being nothing but fluff really isn't deserved. Some episodes are very enjoyable and the animation on the movie is very nice for what it is, if still not perfect. At very minimum, pretty much all fans of My Little Pony are aware of the first TV special, Rescue at Midnight Castle, and most regard it highly.
But I want to focus on overarching world features the series as a whole gets right or does well that isn't quite present or as significant in other incarnations of toy line. These are all things that have always made an impression on me.
1) MLP & Friends is fantasy is a very traditional sense: dragons, castles, princes and princesses, monsters, witches, magic, and lots of stories about journeys and quests to find magical items or save someone. MLP is about magic ponies; traditional fantasy seems like it should be a natural extension of the concept, and yet only the very first series seemed to be able to maintain that setting and concept in just about every episode. Seriously, even the one episode about the ponies getting a puppy is about them finding a giant monster puppy and keeping it.
2) Villains with real power, and a number of them are female. There are a lot, not all well written, but still, they're there and the ponies have to face them often.
3) The ponies mostly don't live like humans. Again, magic ponies. That's the appeal. If I wanted to watch humans do human things, I'd watch something else (I'm looking at you MLP Tales. And FiM? Watch it there...).
4) Non-traditional family structure. I never see MLP get any credit for this, but the first cartoon had adult and baby ponies, but no marriage or even single male-female family partnerships, and the babies were raised collectively by all the ponies and Spike. In fact, even though many of the baby ponies are identical to the mother, and thus we know who at least one parent is, I can only think of one potential time where an adult pony mentions her baby specifically.
5) Spike. One of two reoccurring male characters, he lives with the all-girl ponies, even taking care of the baby ponies, yet never this is never presented as something negative or shameful or not masculine or good enough. He never complains about it, seems happy to be there and do what he does, and even when he does spend one episode trying to find and be more like other dragons, his worry has nothing to do with his gender. He's totally accepted.
6) Virtually no romance for the ponies, except one, Heart Throb, and even that was infrequent. Now, there's nothing wrong with romance, but it's nice to see shows without it too, especially given the (often unfair) stereotype of girls shows being nothing but romance and fluff.
7) No main character. Yes, lots of reoccurring characters, but I actually like that the episodes are free to focus on whoever or whatever they want.
8) Diversity of personalities. It's not as strong as FiM, but the ponies themselves are distinct, don't all get along, aren't all always cheerful and friendly, and can be kind of rude and harsh even. And it's nice to see all of this presented to girls as a normal range of personalities, emotions, and expressions without being exaggerated or having to learn to be "nicer". Also, none of the personalities are "fashionable." Sorry Rarity. And G3 Rainbow Dash.
9) They're all a bit chubby (Same for MLP Tales). Now, yes, much of that is just the art style, and it doesn't have a diversity of body types and hair styles like FiM, but the majority of that diversity is standard-thin or tall and thin, so I don't know which is really better here.
10) It does all of these things with an almost all-female characters. This is rare and also important. There's nothing wrong with a mix of genders, but it's a different dynamic, and all-female is so frequently written off and mindless and "girly" that it deserves recognition when it's really not.