I know what you mean about the lack of highlights, this was a concern of mine whether to go with straight comic style or enhance it.  The forehead needs work - it's supposed to be a wave of hair coming down but obviously that isn't working.  I'm not sure what to do about the shoulders, the one reference pic I looked at had these sticking up above the actual shoulders.  Anyway, I'll check those examples you cited and see what I can do.  Thanks,

 The face structure is poor - eyes slanting up, forehead too thin, ear too far out etc. You have a great opportunity for highlights since this is metallic mostly. Check out chaos engine, speedball (amiga games). Until you get the face structure right then there won't be that contrast you say you wanted. That said I do like the lines for iron man's head. Shoulders too thin,

Thanks a lot, I spent the majority of the time trying to figure out what to use as a BG... :)

Good work man.