Sionak posted:

Ha. They've been working on this for a long while, I think before CoC 7th edition was announced.

Delta Green seems to me to be primarily about the themes while making sure the system doesn't get in the way. The primary theme, of course, is Mythos horror meeting modern fears. (While CoC is traditionally focused on the 1920s.) In the 1990s that meant UFOs and suspicion of our government. In 2014, we have a much better idea about how far our government will go without our knowledge. Corporations are also a lot more obvious in their influence - yet are intangible, ruthless, and resilient. This makes them (as noted by Kenneth Hite) a fair bit like certain Mythos monsters.

So they're updating the themes, adding in a lot of new threats, and generally polishing the game to where they want it to be. By making it their own thing, they can do that without running things past Chaosium. You're right that it doesn't seem like a huge departure from BRP CoC, but I don't think it's really meant to be.

I'm pulling most of this from a couple years' worth of GenCon panels and a GenCon playtest game with one of the authors, by the by. If you're interested, you can hear the panels yourself from the Unspeakable! podcast.