Here we are, at book two in the Underland Chronicles, Suzanne Collin's MG series published before The Hunger Games. General consensus seems to be that The Hunger Games was far better, and while I agree that this wasn't as good, it's still certainly a worthwhile read, underrated among Suzanne Collins fans.
The biggest reason being that Collins's wonderful plotting skill is on display once again. While the adventures occasionally felt episodic, the pacing was fast and consistent, an important feature of MG fantasy. It's also genuinely unpredictable, which is pretty rare for MG, since kids are so bad at predicting things. But the plot here is constantly surprising, with a great prophecy twist (and another twist that I'd call one of the best I've ever seen), a plot that manages to be simple but still interesting.
I suppose it works so well for the same reason The Hunger Games worked so well: Gregor is a nice hero to see the Underland from. He could be a bit annoying at times, but his characterization remained strong, and I can see him growing as the series goes along. The side characters aren't quite as consistent. Some of them were just as interesting as Gregor - of particular note is Ares, whose banishment is realistically handled, which makes him sympathetic. But some of the other characters were... not so interesting, to say the least. Like the fireflies that we meet, for example - their only purpose seemed to be to annoy everyone, the audience included.
As with the first book, the writing was pretty good, except for the fact that Collins tries to be voicey with the third person, which I've always found annoying and never found effective. It's not constant, and Gregor's voice doesn't exactly jump out at you, but it still feels out of place in the third-person narration. But other than that, Collins's prose is strong and well-written. It won't blow you off your feet, but it carries the story quite well, and it's mostly effective.
I'm finding that I have the same issues and merits that I had with the first book, although I'd say that I like this one better. I suspect that the entire series will be enjoyable as this one, which is why I'm going to go ahead and recommend reading, even after just two books. It's no Hunger Games, but it's well-written and well-plotted. That's more than I can say about a lot of other books.