Doesn't the fact that it's concept art imply that it does not show the final style?
We've already seen the amount of detail/style they're aiming for the environments anyway, and I'd expect that, given the amount of areas they're going to work on, the concept artists will focus more on conveying concepts and layout for the 3d artists (? dunno who handles the 3d rendering) to turn into actual pre-rendered levels. Which will then be touched up again by artists, from what I understand.