I thought I might be in a decent position to review this movie because I used to be a big fan of the show, but stopped watching a few years ago. Which means I'm very familiar with the universe and characters, but no longer look at it through rose-tinted glasses.
All in all, I would say the movie was OK. It's not a classic Pixar, but not a Sony Pictures Animation movie either. There are two big issues that (in my opinion) holds the movie back; Character abundance and pacing.
This is a fairly short movie, yet it is jam-packed with characters, both old and new. We are re-introduced to the main characters at the beginning of the movie, but because there are so many, we don't have time to truly get to know them. Someone who isn't familiar with the show's cast would probably just see their caricature from this rushed introduction.
The same problem arise when our main characters are thrown into their adventure. We go from place to place and meet all kinds of new characters. Both the new locations and cast are interesting, but we just don't have enough time to become familiar with any of them. The main cast's interactions in these new environments are as you'd expect from who they are and the themes of the show, which works very well. Sadly, the super speedy pace took away some of the plausibility of their influence. You'll ask yourself "would this/these character(s) really change as quick as that?". If only we had another scene or two, a change of heart would fit the narrative perfectly, but it just felt too quick and easy.
And then there's a pivotal moment in the movie that could have been so much better if only the movie had taken its time to build up to it. Twilight Sparkle's home is in dire peril. As Equestria's last hope, it's only natural that she is getting more and more worried and desperate. So much so that she might do something drastic. Unfortunately this growing desperation isn't shown, so when the moment comes, it doesn't feel like she has earned it. I thought this was the largest problem with the movie, which is really too bad, because I don't think it would have taken all that many added scenes to show that much needed character growth throughout the film.
Of all the new characters, Tempest (the villainous pony) was clearly the most interesting and fleshed out. Her arc in the movie was great, yet I would personally have liked to know even more had there been time. The Storm King was fine. We didn't get to know him as well as Tempest, but he was the kind of character that benefits from our ignorance, so I thought they did a decent job with him.
Other than these points, I'd like to mention the animation, music and performances were all great. It's faithful to the show and throws a ton of references in there without letting them get in the way of the movie's progression. While some of the gags and visual humor were fun and fit the source material, I thought they gobbled up a bit too much screen-time considering how short and fast-paced the movie was.
In summary: I don't think there's any doubt fans of the show would enjoy the movie. The rest of its target audience probably would as well, but would a parent or friend who isn't familiar with the source material like it? My guess is, there are too many characters and too little time spent on each of them to really get into it. However, I think most people will be entertained enough to sit through it without any discomfort. You might have to brace yourself for a bunch of pony-puns though. Also, Pinkie Pie.
