Technically, Cry of Fear is a GoldSrc mod (the engine used for Half-Life 1). It pushed the engine to its absolute breaking point to achieve effects that shouldn't have been possible. The roughness of the graphics and the occasionally stiff animations actually add to the experience; it feels raw and unpolished, much like the human psyche when it is breaking.
As the body's "fight or flight" response reaches its peak, the individual's vocal cords and respiratory system are also affected, leading to the characteristic "cry" or scream of fear. Cry of Fear Full 1.55