The story is engaging, and the problem is simple and easily fixed. The fairies all work together and are supportive of Ruby when she is the one to identify and fix the problem. There is a nice lesson about helping others, and a reward for initiative and hard work.
The pictures are colorful and clear. The characters are easy to identify, and the backgrounds don't interfere with the text.
It is nice to see diverse characters in a beginning reader. I don't know that there were many books like that twenty years ago when my daughters were learning to read. Ruby appears to be African-American, Luna could be Latina or Indian, and May breaks the princess/fairy mold by having short hair, a leafy green outfit, and an androgynous appearance.
There are three books in this series so far, and considering that many early readers will go through lots of books, this will keep them reading for some time. It also provides ample inspiration to young imaginations and may inspire some magical role playing.