Let me start by saying that this is a great read (not just for the Zombie genre, but for books in general) - it has great pacing, a great story, good characters who are deep enough without getting bogged down in exposition fleshing them out too much, and good action sequences.
My only complaint is how the author chooses to end some of the chapters (in this book, and the sequel as well). I love chapters that end on cliffhangers and pull you into the next chapter (The Hunger Games by Suzanne Collins is a great example of a book with amazing cliff-hanger chapters), making the book near-impossible to put down - and I believe that this is what the author was attempting to do in many instances, however, he often flubbed it. Instead of creating cliffhangers that pulled me into the next chapter, the author sort of gave away spoilers - take this example from the second book:
"The four of us said a short good-bye and rolled out.
If I had known what was going to happen, those good-byes would have been a lot longer."
This was maybe the 6th or 7th time while reading this book and the sequel that my mind screamed out "Dude...SPOILER ALERT!" when I hit a chapter ending. Now, instead of being dragged forward to see what happens next, I already know that trouble is straight ahead, and someone (or lots of someones) that we know will be dead very soon...total bummer!
Other than chapter endings that give away a little too much, this is a great read - and definitely worth the price...especially since it is free...and the second book is well worth the $5 that it costs!
I highly recommend both books to anyone who loves the zombie genre, or is a fan of great action/horror/military fiction.