It's nice as an early entry in its genre, but worldbuilding and character development is extremely lacking. The entire thing is very rushed, which is the case for the manga it's based off of as well. I would have liked to see this paced as a TV series instead of an hour-long OVA. The basic premise is interesting (though nothing we haven't seen before) and the atmosphere is nice, but the OVA simply doesn't have enough time for the story it's trying to tell. It's a charming little movie that's worth a watch, and I personally enjoyed it, but don't expect anything super deep and fleshed-out.