Like others have said, this book is particularly amazing in how it portrayed women. Depictions of women in the 1950s were predominantly "women are weaker than men, they should stay at home and care for the children" and Japan was no exception to this. For a manga to dare to say that a woman not only could do actions typically associated with men, but that she SHOULD do them... well, it's pretty daring and that's part of the reason I love Tezuka so much- he's not afraid to take chances when it comes to political and social messages. After all, BlackJack is full of them. 
 The artwork is one of my most favorite parts of the book, being gorgeously retro and still setting artwork standards, showing that you can have a great plot line AND great artwork at the same time. Even if you're not drawn in by the story, it's still worth it to flip through the volume. On an interesting side note, I've heard that Betty Boop had a sizable influence on Tezuka, which you can definitely see in the artwork for Sapphire. Story-wise, it's fantastic. I will admit that the jumps between chapters can be pretty abrupt, which pushes me out of the story a little, but otherwise it's very good. I couldn't help but read this all the way through, sacrificing valuable sleep hours. 
 If you're a parent worried about violence or sexuality, no worries. The book is fairly clean. There are people getting hurt and the book does feature some deaths, but it's far from being gratuitous or gory. By today's standards it's squeaky clean. 
 Overall this is well worth buying for any Tezuka fan or for anyone who just likes a good story.