The cinema of Robert Zemeckis is simply AMAZING! People may knock him for making films that are both technically astute and successfully commercial but that is a subjective point of view. One thing no one can knock is that Robert Zemeckis can tell a great story!
As for the book by Norman Kagan, it is TERRBILE! I suspect Norman Kagan used the name Robert Zemeckis to sell more copies of the book. For when you actually read the book, like I did, Kagan spends more time telling us why Kagan thinks Zemeckis is a hack director and his films shallow. It just baffles the mind that someone would write a book only to try to discredit any talent the director might possess. Any insight we get into the technical aspects of Zemeckis's films are very superficial and actually have been taken from other sources. Kagan is more interested in Zemeckis's personal life and actually tries to psychoanalyze why Kagan thinks Zemeckis made the decision he did regarding each film. If this is serious research and critcal film studies, than it surely proves that some (not all) critics like Kagan, are fat, acne-ridden child-men who envy the seemingly easy success of others while they are condemned to write about it rather than make films themselves.
If you truly study Zemeckis you will realize that he had many commercial failures early in his career but more importantly he never gave up. Before Romancing the Stone, Zemeckis couldn't get arrested in Hollywood, afterwards, he was able to make Back to The Future. A film that you may say is dated, but is great example of the perfectly crafted script. The rest, as they say is history.
Seriously, if you want the best source of information on any Zemeckis film, watch the DVDs with Robert Zemeckis Director's Commentary ON. Zemeckis and his colleagues tell you exactly how they accomplished not only the technical aspects of his films, but how Zemeckis finds the truth to every story. You will discover the motivation behind his decisions and then see the result, right there in the film. I would even go so far as to say it's better than going to film school.