Nice job and colors! The head is a very good work. Seems like done at factory. But... looking for the character model, the chin needs to be a bit smaller.
I agree with his chin being a little large. I used Sentinel's head as the base and cut off as much as possible. I've thought about doing some 3d models of the heads through Shapeways.....hmmm, maybe I should!
Congratulations good sir; you've out-chinned Derrick himself. Great smooth paint job and amazing head!