Look at all of the bad reviews. How many episodes have they seen? 1 or 2 episodes is undoubtedly not enough to give this anime a holistic and comprehensive review.
Don't let this anime's synopsis fool you. If you take this anime seriously, then its score of 3.91 will be no shock to you. But this anime is not meant to be taken seriously. Its story is actually just a background for the refreshingly candid and original humor. The animation and voice acting are deliberately this way to perfectly fit the anime's theme. It's just satirically hilarious.
Granted, its humor is not for everyone. Mahou Shoujo Naria Girls' humor is very particular, and it expects the audience to have some kind of prior understanding/experience with its type of humor. It's not at all a generic comedy, and it's definitely not everyone's cup of tea.
Each episode is kind of structured in a certain way. The three Naria girls start out in some situation, to which there is often some impromptu comedic conversation. They then encounter a monster, and this monster leads them to enact a scenario impromptu, and as a result of the spontaneity, hilarity ensues. I really cannot praise the voice actors enough. From what I saw, each of their comedic skits was almost totally impromptu, with maybe some minimal guide-lining to make sure that they at least advance the plot a little bit. To be able to come up with this kind of humor on the spot is pretty impressive.
There is also the "main" story, in which the Naria girls need to fill up their Naria power to defeat the evil Ice Queen. The story itself has its moments, and if the comedy was not included, then it might have had the potential to become a compelling short story. It truly wasn't a terrible story. Cliche, but decently interesting.
I think the main thing that is very off-putting at first is the art, animation, and conversational style. To me, it seemed like the voice actors were actually video-recorded, and then they were reskinned in production to become the anime characters. So as a result, the animation seems strange and it doesn't seem well-planned. Most of the time there isn't really animation at all, it's just a still picture with sound effects and a narrative voice-over. And at first, the unfamiliar comedy is a bit jarring because the girls tend to all talk at once with seemingly no direction and no script. But all of these things actually are what contribute so much to the humor: all of the comedy seems impromptu and very candid. The bad animation style, the random conversations; each piece deliberately emphasizes this anime's satirical nature.
Don't take this anime seriously. Don't watch it expecting an emotional, inspiring story. Don't watch it expecting the battle scenes to blow you away with beautiful animation. Don't watch it expecting to learn a deeper moral lesson than its surface implies.
If you want a laugh, and if you want some quality, refreshing, candid humor, this is the anime to watch.