I don't mean to rain on anyone's parade, but cel shaded graphics (as done by eg zelda) only *look* primitive. There's still a ton of fast math going on in the background, and you pretty much need a 3d accelerator card to get smooth framerates. The technique itself is not too complex (a good introduction is
here), but it basically boils down to doing all the usual 3D stuff you'd find in Quake2, but using custom textures and tweaking the rendering settings to get the effect.
Not only games use cel-shading, I've seen it used in the cartoons Futurama and Lost Universe (you can tell because the frame rate goes way up :-D )
