What is Payday 2? For one thing, it's a co-op FPS about crims and their seemingly insatiable desire for money. For another, it's a follow-up to the enjoyable, if uneven, Payday. And, for a third, it's the name of a video by game director David Goldfarb explaining how they've expanded and refined this second attempt. If anything, the question it answers is more: "Why is Payday 2?"