Michiel sheds some light on the rendering technics behind Killzone 2 and explains why they decided to take that development approach. He also gives his candid views on the Internet "Hype Train".
"'Deferred rendering' seems to be the buzzword of the moment. What is it, and how does it differ from normal rendering techniques?
Well, a deferred rendering engine separates lighting from drawing geometry. In a traditional forward renderer, you run a pixel shader to sample the material properties (the texture, reflection, et cetera), add the influences from all of the lights, and write out the complete pixel. In a deferred renderer you write out the surface properties (texture, specular intensity, et cetera) first, and then perform lighting on the pixels in screen-space.
The former technique is useful if you have just a few or very static lights, whereas the latter technique comes in handy if you have lots of (small-ish) lights. Okay, so that's an oversimplification, but it is largely correct.
Killzone 2 also features a forward renderer, by the way, to render certain special effects. This includes all transparent materials, but also more complex shaders, like skin and water. "