I've been so behind in commenting on icons, I don't know if I'll ever catch up!

Anyway. You have awesome taste in characters (though I'm slightly surprised not to see Crichton in there!). I really like the lighting on 4. And 6 is gorgeous, it's gritty but still has such pretty contrast and coloring.
Also for some reason I just love the overall look of 13.

Really impressive work on all of these!