I watched this more out of morbid curiosity than anything else. It should be noted that the sex in here is pretty hardcore, and most times it will actually be rather frightening instead of arousing (unless you're into hardcore tentacle hentai)
However, that's part of what I ended up liking: there's a surprising amount of awesome in this show. Instead of being a straightforward PWP, there's a lot of horror content, and a few definite Crowning Moments of Awesome.
The Story, in a Nutshell: Akitoshi Akishima (through whose eyes we see the story) has been having nightmares, involving friends and classmates attacked and raped by horrifying creatures. His dreams also feature a girl, a warrior who fights the creatures. At the start, these are just dreams, though there are women being raped and murdered in the city...but then the girl from Akitoshi's dreams shows up in his class. Getting a little too curious, he follows her, and after she has to save him from almost being killed, she fills him in. Her name is Ai Kagano. She is a sorceress/warrior who fights ancient, evil creatures called the Yuragi. Yuragi feed on negative human emotions (like lust, fear and anger), and are terrifyingly sadistic, in order to provoke the feelings they feed on. Normally, Ai uses magic to wipe herself and the Yuragi from the memories of people affected by the events, but Akitoshi is strangely immune, and he quickly finds himself dragged into the fight to stop the Yuragi infestation in the city.
The characters are actually pretty well done. Akitoshi is naive and a little too curious for his own good, but he's basically honest and good at heart. Ai is outwardly cold and somewhat dismissive, but she has a softer side that she shows when no one's looking. Emotionally isolated after centuries of being alone, Ai starts to open up, just a little, to Akitoshi over the course of the series. Some of Akitoshi's classmates are introduced as well, but they're fairly one-note.
The sex scenes are sometimes played for the expected hentai value, but surprisingly often they appear to be designed to frighten rather than arouse, consistent with how the Yuragi operate. Furthermore, while Ai is inevitably raped, it's a beautiful subversion of the way things normally go in hentai (at least as far as I know). Instead of her breaking, there always comes a point where Ai has had ENOUGH, and this usually means an awesome beatdown is about to ensue.
Unfortunately, the fifth episode has yet to be subtitled, but the series remains very entertaining in spite of that. Mahou Shoujo Ai has graphic content (violence as well as sex) that is not for the faint of heart, but for those who enjoy the darker, horro movie tone and can handle the graphic stuff, this show is definitely worth checking out.