It seems like quite a few players are seeking challenges when not actively involved in a mission. I believe the mission side of the game is a very strong driver for playing it, but I would like to be able to step out of the story and practise or test combat techniques without affecting my game statistics. I grasp and appreciate the concept of the game, that you suddenly and completely unprepared find yourself in chaos. But having completed all missions so far, some kind of training grounds or arena, where you can improve your skills alone or in co-op would seriously add fun to the experience.
Something like this was mentioned in last wednesday’s stream to be announced next week. We’ll have to wait and see