I really like the color scheme, and you have managed to capture personality on their faces. Here are some suggestions for you otherwise:
1. Your spraypaint is clumping up. That is what is giving you the dusty look. That is affecting the rest of the paintjob in a bad way. Either use slightly watered down paint in liberal amounts to do your undercoat or try spraypainting somewhere where it is really dry and not too cold. Those are the factors that will cause your spraypaint to do that. Also, use testors model master spray instead of
th GW stuff. I think that it is cheaper and it is definatly better. You can get it at any hobby store that sells models.
2. Take time to clean up your mold lines. Use an xacto knife blade to scrape the moldlines off of your minis. Scrape, don't cut.
3. As far as painting goes you are doing well. You have good control with edges and detail (great work on the ripped arm bits). The next step is learning how to highlight. Check out the tutorial on this site. Its really excellent and if you practice it you will be in good shape:
http://www.jenova.dk/ -- check out the tutorials section of her site, especially the one on blending. There is a bit about layering highlights that you will benefit from.