Killing Floor features some of the most detailed and atmospheric environments you will see in a horror themed mod, and the objective is to make something that is not only visually pleasing, but also rewarding and fun from a gameplay standpoint .
This mod is unique in that it features full support for environmental physics. In a nutshell? If you bump into a garbage can, it's going to fall over. Shoot a computer monitor, and it will topple off the table it was resting on. This adds a whole new level in gameplay and can often facilitate some strategic employment of the physics system, like putting a table up against a doorway, etc.
It is mandatory to have a working and up to date installation of UT2004 before Killing Floor will run.