Delta Green 2 Campaign.

Genre

According to GURPS Mysteries, this is part police procedural, part thriller. This is primarily an investigative game, just like actual law enforcement--there will be foot/vehicle chases, gunfights, violent arrests, and similar exciting action scenes, the primary emphsis is on investigation, interrogation, surveillance, forensics, etc. Assembling useful information on the enemy.

However, playing out the actual length and pace of an investigation would probably be boring. So the PCs will have access to the authority of the law, and to some degree, the assistance of modern forensic science. But don't expect tactical entry teams and high-tech forensics to solve all your problems! That would be boring.

Tone

This will be a campaign of secrets revealed and shadows fleeing as they are brought to light.

Sources

NWoD material of various kinds (Vampire, Promethean, Changeling, the independent books). 

The feel of the campaign is best reflected in:

Michael Mann's major movies (Heat, Colleteral,)

F. Paul Wilson's Repairman Jack books.