Killzone 2 VS Gears of War 2 through the eyes of a programmer
http://www.vgchartz.com/forum/thread.php?id=59585&page=1
"GoW2: Now, before you start sending me hate mail, I know that I cherry picked an example of a good Killzone 2 pic and a bad GoW2 one. Why does the GoW2 pic look worse? First of, notice the trees. Unlike in Killzone 2, they exist. Also, the buildings are growing organic matter and mold. The trees require quite a lot of power to render and conflict with the theme of the game.
Killzone 2: Count how much organic matter you see. Count the number of round edges. Not many, huh? This looks good, but it is just plain geometry. Geometry is very easy to render and take up very little space in memory. Also, notice the similar color scheme. The same textures are being used over and over, and although they look different, it is a result of them stacking multiple textures on top of each other."