I have read this book and Pat Posner's other book, Fantastic Creatures from Greek Myths to my fourth grade class for several years in a row and they've loved it! The illustrations are good, and the stories engaging, beginning with the Olympian theogony (creation/origin story of the Olympian gods and goddesses)and moving through my personal favorite, the story of how the seasons came to be (Persephone and Hades). Each story builds on the other so that by the end of the book, the young reader is intimately familiar with the principal gods and goddesses, their strengths, traits, and foibles.
Posner uses the Greek names, which is nice--other authors, like Pope, have mixed in Roman names for the gods and goddesses--hence Hades is 'Pluto' and Hermes is 'Mercury'. While by no means an expert or authority, I think it's nice to stick with the original names. (You can always learn other names later.)
In brief, here's what I liked:
+ each story is short (no more than fifteen minutes' read aloud, with time for questions and notes, or a good bedtime-story-length)
+ the illustrations are very simple--not overproduced or flashy
+ Posner chose good stories of strong women and goddesses, not just strong men and gods
All in all, an excellent primer for young readers. If reading independently, I believe that most third and fourth grade students who read at grade level should have no problem reading this text. However, I think this text comes alive best when delivered energetically by an experienced older reader who can engage the young reader with a give-and-take discussion of the stories.