Here is my critique you wanted.
- The colouring on Zonk is not too bright and not too dim.
- The logo at the top left is also pretty nicely done.
- The shadow behind him is a nice addition.
- His limbs are rather out of proportion. His right leg is thinner than his left leg. His right arm is longer and thinner than his left arm (and it's also missing a thumb).
- The background is much too blurry for my tastes; which causes the detailed rock Zonk's standing on to look out-of-place.
Overall, I think this is an adequate drawing but you could use some improvement on backgrounds and proportion.