Some things that I notice:
1. The joints don't look like they are connected. Especially true of the upper legs where to me, it looks to me like sheets of metal welded on top of each other. In places like the elbows and shoulder-upperarm connections, it doesn't look like there are any joints at all. It doesn't have to look realistic but I find that art tends to look less "off" if each component has an "explanation/suggestion" for it's existence and how it works if that makes sense.
This robot for example would definitely not actually be able to stand and walk around, but you can see how it would if it could. I think that helps make it feel right when you look at it.
2. I like the general colors, but I think you could reduce the number that you are using. Your hue-shift is awesome looking on the pallet but on the figure I don't think it's working. You have way more colors than you need given the size of each single-color-area.
3. The shape your shading takes doesn't seem to match the intended shape of the volume. For example looking at the knee area, the shadows are round but the shape is rectangular. I didn't do a great job but here is my attempt at how I would shade something like this:
I think you are going for a rusty feel to the metal, which is manifesting itself as the little strokes of shading coming in to each other which I don't think works. Here I tried to make the metal look rough and rusty by adding imperfections to my dithering which I think looks way better than the way I had it before.
I'm not that great an artist but hopefully this gives you some ideas.