The basic game mode, Siege Mentality, involves a lone player, with a full armoury at their disposal, defending a location for a few minutes against a whole team of opposing players armed with short-range weapons.
One map is an isolated, large farmhouse out in the sticks (familiar to those who have played the single player campaign). And it’s fine and fun and there are lots of nice vantage points in the form of first floor balconies.
But what if you change the time/weather settings pre-game to make it a dark and stormy night? What if the defender is limited to a pistol, and the attackers can only use knives? What if everyone is in restricted to first-person view?