The worst feedback someone can give is, "I don't like it." There's no value there. Especially in regards to design. It doesn't provide a way forward, or point to a new direction. Good feedback is critical in nature, but rooted in analysis. It pokes, prods and understands what the designer was trying to accomplish before speaking it's voice.

Design is rarely created to please a single person. Personal likes and dislikes aren't important when analyzing design. What is important, is asking: does this design accomplish its goals, or are there ways it could work better.

By providing informed critical feedback, instead of opinions, design projects will go faster and everyone will be happier with the end result.