Painkiller is a first-person horror shooter, designed to satisfy the gamer's hunger for intense, fast-paced action. You are Painkiller, a mercenary for hire, charged with cleaning out nests of the undead. But an unholy pact with a demon unknowingly puts you square in the middle of a fight for control of the underworld... with the future of humanity hanging in the balance.

• Intense gameplay: The player will be constantly outnumbered, fighting against seemingly insurmountable odds.
• Next-generation graphics: The game uses a proprietary 3D engine capable of pumping out 100X the polygons of some of the latest shooters, while adding increased texture quality and the latest lighting and shadowing techniques.
• Lasting replay value: Painkiller features a standard single player campaign, with additional modes to encourage replay. The game also features full multiplayer support.
• Combo weapons: All weapons come in pairs, with a primary and secondary fire.
• Morphing: Your unholy pact gives you the power to morph into a powerful possessed creature with every 100 souls collected.
• Monster AI: Advanced AI coding will simulate group behaviours. Monsters don't spawn onto the map, they patrol. They are constantly aware of the player, and will coordinate their attacks by retreating, regrouping and counterattacking.
• Physics Engine: Painkiller employs the Havok physics engine, allowing for inverse kinematics ("rag-doll physics") and deformable, interactive environments

Official fact sheet from People Can Fly.