Wow. This is one of the best books I've read relating to Buddhism. The author does a very good job at taking you from the very beginning and walking you through the core concepts of Buddhism and explains them.
I'd say this book is perfect for someone who has taken the three vows, or someone who knows a bit already but wants a good starting point, then this book is great for that.
I don't think I'll ever be done reading this book. I keep going back through chapters and rereading things and always feel like I missed things from when I first read it. I can't wait to get the other two books.