First off: SPOILER ALERT!!!
Since this is the second book in a series, talking about it might spoil the first book, The Hunger Games. There may also be some spoilers of the second book as well.
I really like this series. I haven't read much young adult literature as an adult, but I've been reading more lately. I've been doing this because I think that some of the most interesting story lines are in YA books, and I like a good story line and a fast read sometimes. However, I think I like this series beyond that, and here is why:
1. I have always been a fan of dystopian literature and satire, and I believe this series adds something to both of those genres. I think that the world of the Hunger Games series is well drawn. I think that the books also offer a critique of consumer capitalism that rivals many novels for adults. As a point of comparison, I am currently read Scott Westerfield's, Uglies and I like the book, but I think it's futuristic world and the trials and tribulations of the characters offer not original or genuine critiques of society, but obvious platitudes and lessons in behavior for teenagers. I don't believe that Collins does this. I mean, come on, it is a book about a revolution, with some great real, history reference points.
2. To further develop that idea: Katniss is a flawed character. She isn't 100% likable. In fact, Collins offers Peeta to the readers as a foil for some of Katniss's less endearing qualities. It would be easy for Collins to write a book about a world that is controlled by a bloodthirsty government who oppresses the rest of the country and uses them for the fruits of their labor and natural resources while they live a life of excess in the capital, and the answer to solving the problems of that world is to be a good person, or to refuse to stop being yourself, or some other platitude. This is not the answer she gives. Katniss is driven as often by selfishness as she is by any desire to start a revolution, or bring about peace. She loves the people in her life and loves them fiercely. This is a real human characteristic.
3. It is quite well-written. As someone who really does value craft and form, some YA novels make me cringe - a lot- while I read them. They are havens for cliche and purple prose. This isn't. I think I only cringed once.