Think of siege's tactical and methodical gameplay but apply it to a PvE co-op shooter. The main gameplay loop is going through zone and eliminating target till either you get to the objective ore till you feel the risk is minimized enough to start it. Any health lost will remained lost until you gain enough experience in your next few incursions to heal the operator, If you lose health you go MIA and you'll have to recover that operator to use them again. You gain experience throughout these to get new equipment for all operators and some for the individual operator you used to progress them. It's a rough overview but that's the gist of it.