Critiquing calligraphy is something that I feel is learned by more practice. Also learning how to see little details of you work better with each piece. One major thing is learning how to see different angles that your pen should be at while constructing each letter.
Another thing is being able to see the spacing that is needed between each letter. Because if you are writing a word and the letters are crashing into each other it will not be a solid piece. This video is part one of a two part series of me explaining how to critique calligraphy work.