Cost effectiveness: Is this design cost effective?
Does this design have the same look – durability, style, ergonomics, etc – while reducing the overall product cost vs the competition.
Feature Location: Are the various features of the product in logical and accessible positions on the design? Does the design improve on competitors designs?
Demonstration, presentation, feedback rounds: What does the rest of the team think of the design? What do select beta testers/product testers think of the design?
This actually relates to finishes and colors specifically. Many initial visual prototypes find that color or reflectiveness (matte vs gloss) and texture will all play a bigger role in an end product than they thought.
Square Peg - Round Hole: Would the design be aesthetically/ergonomically/functionally better if there were rounded corners or square corners, triangle holes or star holes? Etc.