Delta Green is the roleplaying result of August Derleth and Tom Clancy getting trapped in a teleporter accident. Full of veresimilitudinous military/intel action in a world where you could actually see humanity interacting with the denizens of Lovecraft's feverish "imagination."
This little adventure plaes the PCs in the ever-unpleasant hinterlands of the Hindu Kush in the even more unpleasant world of 2015 (or thereabouts). It's not a big adventure, but as usual for CoC, the implications of failure could be huge. I was particularly amused by how it takes account of likely PC actions like calling in airstrikes, using drones and trying to run off on their own...
Advantage: It's so realistic!
Disadvantage: It's so realistic!