Question: While reading this wikipedia [article](http://en.wikipedia.org/wiki/No_Silver_Bullet), Brookes has told that there is a difference between "good" designers and "great" designers. What is the difference between them? How can I decide if a designer is good or great?

Answer: 
A great designer catches the intent of what I want to accomplish and improves on it to my delight. A good designer follows a specification to the letter, but creativity shows in how they did that.

A bad designer is, well, none of the above. 

I think 'exceptional' is always in the eye of the client, and the people they hope to reach.

Other things come into play in the 'great' category, such as someone who can articulate why my 'vision' of something might be skewed. I guess it boils down, mostly to how much ownership someone takes in any given project, given a group of people with similar skills.

Great, is also, entirely subjective.
Great designers can make 2 + 2 = 5. They change the art of the possible.