Very cute book. The story has only just begun. This book reads a lot like a young adult. It only mentions a few times that the characters are middle school aged. I know some about Norse mythology, but this book does go into explaining the myths, so if you are not familiar with it, don't let that scare you off. This might even be a good and easy way to learn more about the Norse myths before moving on to an adult series about the Norse. I'm going to look for some.
If you don't mind YA books, then this would be a good book for you. If you don't like YA, then I would stay away from this. I will say that so far there hasn't been any romantic entanglements, though one person mentions that she has a boyfriend, but we never see them together.