I have been hearing about Delta Green for a while now, listening to a few Roleplay podcasts and getting into the theme of the game. I am interested in running some Delta Green campaigns soon, and someone recommended this book if you were "Wanted to see the progression of the organization through the years." It is a collection of short stories that take place from shortly after the inception of Delta Green all the way up to present day. Each is set about 5~15 years apart. Being multiple short stories by different authors, the book didn't have time to slow down. While I found each one pleasurable in its own way, if one story isn't to your liking, a new one will pop up soon. If you're looking to get a nice, rounded picture of Delta Green, or want some inspiration when you run your own games, these are a fantastic introduction. My only recommendation would be to find a rough timeline of the history of Delta Green. It goes through several organizational changes from the 1920's to today and the stories, while remarking on these changes, do not lay them out explicitly. So having a rough idea of what shape the group is in during the time period each story is set in enhances the plot a bit, but is by no means necessary to enjoy the book.
[5 of 5 Stars!]