Killing Floor requires much more coordination and teamwork imo, at least if we are talking about higher difficulties which is the meat of the game. I mean, you have different classes with dedicated roles, one guy heals, one guy welds doors, specific classes have to kill specific zeds (sharpshooter, berserker for scrakes, support for fleshpounds, demo spams pipebombs etc). If you play Suicidal or HoE each member of your team has to be very careful and the classes must be balanced and max leveled. Of course there are some known strategies that everyone follows but they are strategies nonetheless.