The parts are semi-transparent as received; this will vary with the type of material you specify.
Giving them a coat of Tamiya primer shows the detail available, which is otherwise hard to pick out on the translucent surface as received.
The grainy texture of a cast block is reproduced nicely, but in the right light, you can see the regular step-wise grooves that arise when the printer head scans back and forth, as in the oil pan or valve cover.
Fixing this could involve light sanding, or one could assume that paint will fill it. I'll try sanding parts where it will show (oil pain, valve covers), and simply apply paint where it won't (bell housing) in order to evaluate the importance of the roughness.
The level of the roughness is noticeably less than in the adjustable wrench made using a $250,000 prototype machine in a university mechanical engineering lab about 10 years ago, but is still visible on close examination.
I am guessing that a 3D printed body will not be as smooth as styrene or a good resin body. The advantage over resin is low porosity, high dimensional accuracy and no mold release agents. Styrene remains the best quality if you can get the specific parts you want.
The area of improvement is now at the level of building ever finer printer jets, and stepper motor drives with smaller step sizes to bring tracks closer together. I suspect this will proceed rapidly; take a magnifying glass to output from a good inkjet printer on decent paper and compare to the late, unlamented 8-pin dot matrix printer. As well I am assuming Shapeways is using commercial-grade printers, i.e. better than the $1500 home hobby unit from Micro-Mark, but substantially cheaper than that $250,000 university prototype of 10 years ago.
So we are getting closer.
I'll paint and build up the motor and keep you posted.