I had been hearing a number of things about the Delta Green stories and decided to pick this up as an introduction.
The first thing that caught my eye was how each story takes place on an ever progressing timeline, right up until sometime in the future. It is an interesting concept and helped to move everything along as one read through the collection. As each and every person was dealing with the mythos on some level, it was interesting to see someone tackle how they would in each time period.
Most of the stories in this collection are excellent, with only a few that were a bit boring or uninteresting. Detwiller did a good job mixing things up from story to story, mixing the horror up between mythos creatures to Lovecraftian horror and everything in between the two. Overall it was a very nice mix, and kept me engaged throughout the entire book. At no point did I feel that he was more interested in one type of horror over another, and in many points, he did a good job showing that sometimes mankind is the true monster, which I liked.
The writing in this book is handled well, and Detwiller also changes up his writing style for a couple stories which keeps it interesting and engaging. There was maybe one or two stories where it didn't work so well, but in the grand scheme of the collection they are easily lost among the better stories.
All in all, this is a good collection of stories that I rather enjoyed. There was less material about Delta Green as an organization then I was expecting, at least until the blurb at the back of the book, but it still gave enough that any Lovecraft fan will get their fill. This is also a good book for those into military horror stories.