It's hard to imagine blockblustery first-person shooting today without Call of Duty 4: Modern Warfare's online progression systems, which - inasmuch as you can assign this much clout to a single game or developer - transformed the genre back in 2007 by reinventing multiplayer as a kind of RPG. Shooters without COD-style gear levelling ladders do exist, not least Counter-Strike 2, but most of the juggernauts depend on such fixtures, especially now that free-to-play service models have become the norm. So it's jarring to hear from Mackey McCandlish, one of Modern Warfare's original developers, that the old Infinity Ward team were split over the act of using XP to unlock guns, with some worrying it would be "unfair".