Let me start by saying welcome; this is a good place to be if you want to expand your arsenal of pixellery. Let me follow that by saying you have skill; more than most, if this is your first go at pixelling. Your technique is very good, the design is cool, and you've kept it all clean and readable, even given the minuscule proportions.
That said, this looks to me more like a stuffed thing (a ragdoll, maybe?) then a robot. The colours, combined with what I read as a squishy bulge near the stomach makes it look too soft.
Here's an edit (I hope you don't mind edits...):
I changed the palette (obviously), though I used only your original grays + white. Makes it seem more like it's metallic, I think. I also made the eyes white, as it gives them, imo, the impression of being lights or something... glowing, anyhow. I got rid of the aforementioned bulge, as well, and made the body a bit more geometric. Changed the jaw, too, 'cause I get carried away like that
I think the stuff I fiddled with is valid, unless the original design (soft appearance, etc) was intentional, in which case forget what I've said. Technique wise, you're good To go, as I mentioned. Good stuff, and good luck with this.
