I finished this the night before it won a Newbery Honor, and I'm so happy that it did. I liked how: 
 - the character of Ada gave you so much hope for her future, from almost the very beginning. She was realistically damaged yet optimistic. Her story is very satisfying, and will be especially so for kids who care about injustice (which most do). 
 - Susan is a complicated adult - something that might not be so familiar to younger readers, who mostly see a fairly standard parent character in books. 
 - the war is constantly, increasingly present, yet realistically also often in the background for a child. 
 I actually didn't think the writing itself was so extraordinary (though it was very good), but that the story itself was well-done and unusual.