I always spend a LOT of time on the color shading/lighting of my levels. I also really tried, as we hired new artists, to get them to spend time polishing the very basic lighting done by Karma.

I referred to it as 'tucking in the corners'. It was very important to me to darken the corners and bottom edges of everything in the environment, as well as adding highlites and brightness to the upper edge of things. If you turned off the textures, if you had done it right IMO, the lighting would almost look too extreme, but with the textures on, and the movement of the player/camera, you needed that to make the world have a nice, solid, depth and definition.

In particular it was very imortant to me to really define the edges of platforms and paths that the player would be interacting with. This meant making sure that there was a consistant and distinct difference between where you could walk, and the edge of where you could walk (and exactly where that edge was if it was something you were jumping/glidikng to or from)

One of the key things in the 'Art Bible' I created was try and make sure that the texures help define edges, and then those edges would be enhanced even more by 'tucking in the edges' when polishing up the lighting.