This was a great sequel and I'd say the author is one of the most skilled people writing in the genre today. I'll be the first to say that the first 50% of the book was a mixed bag of enjoyment for me for various reasons, but it ended strong.
I usually don't go too in-depth with character, plot, etc. for sequels since I give an initial breakdown of those impressions with Book 1, but I think I'd like to expand on my first review a bit.
The Characters
I wasn't the biggest fan of the characters in Book 1, and I can't really say this book changed that. But, the characters don't feel flat. So while I would probably find it annoying to spend time with them if they were real people, they still felt like people that could exist. The fact that I wasn't overly fond of any of the characters tempered my enjoyment a bit, especially during the slower parts of this book.
The Plot
This is what kept me reading. The situation escalated, turned up the tension, provided a few moments for the characters to catch their breath, then threw the next thing at them. Structurally, this was a well-crafted story. I also liked that the aliens resembled more of a "traditional" alien threat in this book as far as their appearance went. While copy machine, refrigerator, and fire hydrant mimics can be unsettling for a moment, they lack the cool factor to approach an action scene with a straight face for any amount of time, at least for me.
TL;DR
If you enjoyed the first book, you'll probably love this one. Unless you have a mimic fetish, then you might just wax nostalgic about the good ol' days. I look forward to the 3rd installment of this series to see what's next as the characters likely enter a new stage/phase of scale in the universal order of things.