Very good stuff. My personal suggestion would be to limit the use of black pixels as outlines in the super monday night combat pros pictures. I prefer the ones from the fist two games because they have no black outlining. Also those trees are wonderful.
Like gaboloth wrote, the black outline is nice on a one color background. If the models are inside an environment (like the in-game screenshots), they will look like they're apart from the environment, which is not what you want I think. Concerning my personal tastes, I absolutely love the SMNC models ! for the screenshots, I like the medieval trees and wall blocks, and the robots of the first game (they remind me of the Tachikomas from Ghost In The Shell).