Excellent second book-- it flew by for me, and I honestly didn't see many of the plot twists coming. I have to admit that the end baffled me.... I was there before I realized it-- and with so many questions (as I'm sure Collins would have hoped!). All I can say is that I'm really glad I'm reading these AFTER all three have been published. If I had to wait for Mockingjay to be released, I would be ticked off! 
 Having said all this... let me address it from my "teacher hat" standpoint. I began reading these books because I teach some 10 year-olds who were reading them. After The Hunger Games, I could honestly say that I felt some of those kids could handle the book IF they had an adult to discuss it with. I don't keep the books in my classroom library, because I believe they honestly need to be something a parent makes a decision about for kids the ages I teach. I would have to say that this second book was darker, more violent, and harder to stomach-- and I really would NOT recommend it for the kids in my school. Middle school age seems to be about right for these books, and if a parent of one of my 4th or 5th graders asked my opinion, I think I'd suggest they try to hold out for at least another year....