I probably do more mental critiquing of biographies than of any other type of book I read. I've never been a fan of the bio that starts waaay back with the birth of the subject's grandparents, and I wish more biographers would start with the novelistic convention of bringing us into the action that the subject of the biography is best known for, and then gradually working the earlier history into the narrative. I also find myself wishing for more creative plotting and formatting. Although a life is lived chronologically, a biography need not be presented that way. Also, every year of the subject's life does not deserve equal space in a bio. Some years are more eventful and significant than others.
I critique books, I also turn the points of the critique back onto
myself and my own work. I'm not writing biographies, but I can still
push myself to think beyond chronological sequencing, to start at an
interesting place (which is not necessarily the protagonist's birth or
even the start of his/her day), and to compress or delete the slower
times in the characters' lives.