The theme interpratiation was both that stores are generaly pretty calm untill there are big sales happening and also the general gameplay is calm when there are like 2 or 3 customers on you but either when you run through a lot of them or an alarm starts blaring dealing with a bigger hoard can be a frantic chasing of new weapons and trying to keep the enemies at bay.
The game ends once you go back to the entrance and escape which can be done by just holding the "E" key on the "poly station 5" stand and then following the arrow back to the entrance which unceremoniously throws you back to the main menu.