It really surprises me that noone has done something like this before:
When you get down to it, this is just a FPS playing in a no gravity environment, with full 3-dimensional movement on demand (eg you have jet packs to move around w/ as opposed to having to used stationary objects such as walls to jettison yourself off of). I can't imagine gameplay for this is much harder than aiming to where you want to go/shoot using the right analog, and moving in that direction using left, with buttons to actually shoot and lock onto the nearest floor. Hell, were it not for that last 'locking' bit, this game might be easier to code than a traditional FPS because you don't need to worry about gravity at all, whether for the players or artillery.
Every creative and scientific work in history is the result of expanding upon whats there, and adding to the common body of knowledge and works as constructed by our ancestors. This game just goes to show that it doesn't take much to make some thing new and creative.