too much going on...
well, my main crit on the first one is that there are way too many greebles(little panels and details and bolts, whatever) and it gets way too confusing. use them where they make sense. don't just through panels and bolts and wires because more detail is needed. i find it the opposite. less is more. just put them where they make sense, and they'll have a better effect. for example, the shoulders are pretty cool looking, but i don't notice the shoulders as much because of all the confusing stuff going on in the neck area. the shoulder would pop a lot more if that stuff wasn't there. another example is the elbows... the one on our right has a few less panels on it and looks a lot better than the one on the left. the knees are cool looking, but again, they get lost with all the stuff going on in the thighs and and boots. if the arms are cleaner than the chest plate stand out more. hope you get my point. remember, try and keep it simple, that way the important detail stuff sticks out, instead of being jumbled with everything else.
your second pic is much better for all the reasons i just described.
the last pic has to many middle values in the forground and such a dark value in the mountains in the background. that leads the eys to the mountains and it's hard to even keep your eye on the characters long enough to tell what's going on. so rememer, you want your highest contrast, darkest darks and lightest lights, in the foreground and the middle tones should be left to the background.
hope this helps.