I agree with Margenta. The materials in the scene–especially the table cloth–are very good, but you’ve got some great character on the robot that’s missing because of the shadow crossing the face. This is generally a no-no when doing portraits of some character.
To add to the critique, however, I feel the need to point out the materials on the robot. It seems the surface of the robot’s head is a bit less detailed than the scene around it. I understand that you’re coming from a cartoon reference, but against the rest of the scene and its very high fidelity, the robot–in particular the head’s materials–seem pretty flat. But that’s just my first impression…I don’t know what could be done to liven it up. Perhaps it’s fine the way it is, it just seems to fall away against the detail of the scene it’s in. Perhaps adding a bit more geometric detail–but then you’d be departing from the original design too far? Oof. I wish I could be more help in my suggestions…I can only give my impression on this.
The problem with the butter was already addressed well.
And that’s it. You’ve got a really eye-catching scene right now. If you stopped here, it would be good. But putting a couple of tweaks would put this in top-row contendership for sure.
Awesome work on a cool concept. 
Dan
