People have given you great advice already. I don't know if I'll be able to offer anything as good as they did, so I'll try to point out specifics.
I think I'll go with themes the others brought up and detail what I see. First, maybe you could work on perspective. For example, the character's right foot looks like it's pushing against the floor on the inside part of it (the left side of the foot itself), but the foot mass in itself doesn't follow it accordingly, so it ends up looking like having a slight different form than the other foot. I'm sorry, I'm really struggling with the limitations of my own English (not my mother language), but I hope this makes sense. His left arm, the upper part of it, right beneath the shoulder thing, also looks a bit off, perhaps spun too much to the left...
The mechanics deserve some development as well. This is hard and requires meticulous training and a large repertoire in your head, but look at the guy's abdome, for instance: it seems he's twisting his "spine" to his right-front side, making it shorter to the viewer's left and longer to the viewer's right, but then, if those are metal parts, they could't simply be shorter on one side, they'd have to overlap (and be of different sizes so that they could fit inside the other when overlapping). Here we see them as being some elastic material, like skin or tissue, but at the same time having lines that suggest that these are different pieces put one over the other.
The hands, especially, deserve some more love, care and understanding...
The line work in general also deserves some more love. I guess that the natural way to go would be to vary line weight according to light direction, position, distance from viewer, weight etc. (think of Jake Parker's stuff--which is great, of course). If done right, this 9 out of 10 times results in something beautiful, but I also think that some machinery like this can get very interesting if treated a bit like technical drawings, with "cold" thin lines but some Moebius-esque light colors and subtle gradients, somewhat like this:
It really looks like outdated software, almost vintage, by the way, but it's not vintage enough to become appealing due to its antiquity. It seems you color dropped a darker green on some parts that were already green before and didn't correct the variations (look at the green on the head, for example): I cannot know for sure if this is lighting or the rough color drop.
These are all things we have to go through sooner or later. Keep going!