I loved both of these books.
Yancy is an excellent YA writer and has won numerous awards. However, I must confess that while other 5 year old girls carried Strawberry Shortcake backpacks, I sported everything E.T: The Extra Terrestrial ( by Spielberg) and since these books are alien themed my opinion might be more biased than normal.
I will tell you though that you will not be bored while reading. These books are action oriented ( there are, after all, characters trying to survive and save the human race). These books, if done right are going to make some kick ass movies. They also would make a not so shabby TV series as well ( hint, hint..tv people).
I hope there is a book #3 in this series soon.