It's a Dark Magical Girl series, probably inspired by Puella Magi Madoka Magica, two years earlier. (Optimistic young girl gets involved in surreal magical girl adventures... but there's a body count, they have to kill the Monsters of the Week and their enemies are fuelled by despair. Also, both shows were licensed by Aniplex.)
I quite liked it. I don't imagine I'll ever rewatch it, but it's quite interesting.
For starters, it's quite weird. It's less predictable than even your average Dark Magical Girl series, let alone PreCure. The magic and symbolism is based on Tarot cards, anyone can turn evil and I don't think Cerebrum (the Big Bad) ever lies. Talking to him is a terrible idea, but every poisonous thing he says is true, at least from a certain point of view.
The protagonist's angst is a lot more convincing than usual. It's normal in this kind of show, leading into the finale, to try to break the Indestructibly Pure and Kind-Hearted Heroine. Normally, it's a foregone conclusion. Here, you expect it to work. Cerebrum's tactics against our heroines are sharp, evil and (because he's Cerebrum) honest.
I like the balance between light and dark. The show's faithful to its heroines and their good-hearted worldview. There's a lot of darkness here, e.g. the possibility that our heroines and their foes both serve the same boss, but it's not one of those shows that goes so gratuitously dark that you just switch off. It's about its characters. They grow, e.g. with Seira's goal-driven hostility to empathy, or with the gentle Luna's inability to control her fears and insecurities.
I like the art, with its surrealism and its childlike, big-eyed character designs. (Actual ages: 12 or early teens. Apparent ages: maybe eight. Their cup sizes don't fit that, but then again the most prominent examples tend to be facing jealousy or other more adult issues.)
Does the show have a weakness? Hmmm... well, its focus isn't where you might expect. It's not really about beating the Daemonia. Our heroines have to fight them, yes, but it's never clear where they came from, what they're here for or whether it's even possible to stem the rate of infection. They're likened to a virus. Similarly, what ultimately happens to Cerebrum is a bit "blink and you'll miss it" and I honestly couldn't tell you why he existed or why he'd had his goals. The whole monster-beating thing is a sort of very active backdrop to the character drama with Akari, Seira, Ginka and Luna.
This show isn't misery despair porn, although it's not afraid to overlap with it a bit. It's a mix. The characters are cute and charming, but they have to kill despair monsters. Overall, it's a good, solid show. Nothing wrong with it. There are some nice touches, e.g. Laplace vs. Schrodinger. I like the character journeys and the tone of the finale. I think it's underrated.