@Conscience: or Unknown Armies, Exalted, or especially KULT–where God is explicitly described as Mankind’s implacable enemy. The headsplosion would be memorable.
Re: cooperation and diplomacy: in most of the very best games I’ve played, the focus wasn’t on conflict and bloodshed, it was on discovering how to AVOID conflict and bloodshed, and how to turn enemies into allies. Or at least non-enemies. At best, it made the party’s actual goals much more difficult or impossible to achieve. At worst… a bullet in the upper guts does not respect character level. And Cthulhu isn’t in the least inconvenienced by lead slugs.