My 5 & 7 year-old daughters love this book, in a cart-it-with-them-everywhere-we-go kind of way. Four key elements draw them in. First, the pace moves along quickly, and their interest as readers never flags. Second, the humour is frequent and edgy (by first grade standards). I spent a week hearing "I'm going to kick your ever-loving butt!" followed by peels of laughter. Third, the characters are interesting and grow. They have flaws, and learn from their experiences (this also makes for great reading coversations). Fourth, the images are well-drawn and in colour.
While we read many other things, both my daughters have heartily embraced graphic novels. Giants Beware is a great pick for fans of Amulet and Zita the Space Girl. I only wish there were more graphic novels for the younger set of comparable quality.