I like it :)

"The shading on the main mecanic part (where his torso would be) and the drill are good, but the limbs seem rather flat."

"the shading is too smooth. It lacks texture."

lol, can't please everyone!  For the final version it'll have a blockier colour palette, so the drill bit will be less smooth.

Well the only smooth shading is on the right arm; I'll have a fiddle with that if I open the file again.

Well It's difficult to be picky about reality when dealing with a Big Daddy ... but if his arm weren't counter-balancing his weight, he'd fall over :p  I was trying to get a semi-neutral kind of pose in an isometric environment before I did anything exciting with him, but fear not, when I do his final version it'll be a more exciting pose :)

Automatic gradient :O 

I know what you mean though, saying that it does look a ltitle too smooth, and the light is in an odd place (not sure what I was thinking there).  The left (his left) arm does look a little far back, but that is intentional, its mimicking a specific pose; but I can see why you may assume that was unintentional.

Doesn't look very pixelated when zooming in, looks like it has AA one quite a view parts.