The story isn't great, but I don't think that it's bad, either. It's certainly not a waste of time, in my opinion, especially considering that the art is pretty good. Goraihou Gakuen e Youkoso doesn't have a "main" storyline as of volume 3, but plenty of manga don't (especially in the beginning). It's a cute read, and reminds me of CLAMP School Detectives with a supernatural twist.