I'm moving this to Teen, instead of children's. It's about war. Horrible, violent, gory war. It's exciting, and the action is realistic to the plot--meaning it lets up just long enough for tactical discussion and then starts again. 
 What I really loved about this series as a whole is that it's a fantasy series with no magic whatsoever. Nobody is getting out of dangerous situations by casting a spell of protection or relocation or anything like that. Characters get themselves out of trouble by either fighting or fleeing, which makes sense when you encounter some giant rats who want to kill you. The rules that govern the worldsetting are clearly defined, and within those rules, everything makes sense. No particular class of characters (the rats, the spiders, the humans, etc) is All Good or All Bad--you can't look at any class and say "oh, they're mice, they're all on our side" or anything like that--each character we meet is an individual with an opinion. 
 Collins' habit of appending "said ____" to each line of dialogue wears a little, but I'm willing to overlook that, because I really love this series.