I really like the idea of a high school in Hell and I can think of a lot of other great movies with similar premises like Pixar's Coco and Tim Burnton's Corpse Bride, but what ruins this movie is its execution.
About at the 30 minute mark, it's like the writers just completely abandoned their original premise of a high school in Hell and the whole movie falls apart. There's all this talk about the madness of Able, God appears but doesn't really add anything to the story, and the movie's ending doesn't even make sense.
On top of that, the movie is full of anime cliches like how Rinne is constantly late for school, the student council being the antagonists, and Rinne having this genki girl personality where she's so happy go lucky and optimistic all the time.
Also, a lot of the conflicts in the movie are resolved through deus ex machina. For example, a character loses his arm, but Rinne just tells him to believe in himself and magically the arm reappears because all you have to do is believe you can do something and it'll come true.
The only good thing about this movie is the art. I really like the design of the school and the demon students that attend it. It's interesting how each demon is designed after a different monster like a mummy, a witch, a werewolf, and Frankenstein's monster. However, while the designs are good, the animation is another matter. It's painfully obvious that this movie was made on a small budget; there's one scene that lasts for over 10 minutes where all we see is a clip show of still images.
Overall, I'd recommend do not watch this movie. It seems like some talented people worked on it, but it's so disorganized and poorly executed that I recommend avoiding it.