Lady Gaga was apparently an influence, after Black saw one of her concerts. "Going to her show, feeling really uplifted and energized by that, and going like yeah, I want to get that kind of spirit in the game. Just want to have fun with it -- fun with a gun!" And to accomplish that, Black put things like XP and health orbs in the game that looked familiar if you've ever hunted Agility Orbs in Pacific City. "The orbs are a little homage to Crackdown. I'm a big fan of Dave Jones, I've known him on and off for years, great to see him back making games again."
He also pointed out an in-game nod to Metal Gear Solid (an exclamation point marker on a building), and gave some kudos to Borderlands, another shooter with an arcade bent. "I was quite surprised at how well the [damage] numbers worked in Borderlands. You see it in videos, and you're like, that looks a bit naff. But you play it, and you're like, that's really $*(%ing cool, actually ... That spirit is sort of lost in video games, and we can do that stuff, and we should revel in it."