When working on the physics, our main goal was to create a more realistic experience than in other action-RPGs, mainly to avoid graphic bugs and clipping problems. The result is very nice. A good example is the empty bullet casings; they fly off your gun, throw a shadow on the floor and jump around, with the floor material determining the sound and behaviour. If you stand near a wall, they don't fly through it but jump off the wall - physically correctly. The bullet itself leaves a mark in the wall (if you hit one) - a mark that won't disappear just because you wait a few seconds or shot some more times.