Here's my favourite answer from Crispin Glover's AMA
Because nothing I could possibly write about today could compare to this.
You are my friend Toyou4yu. There are certain things that happened since being in Back to the Future that makes it difficult for me to reflect on the film as having funny things happening. Specifically there was a lawsuit because of something the producers did that was illegal in the sequel to the film. What the producers did that was illegal was as follows. The producers used the molds that were taken from my face from the original film and had prosthetics made to resemble my face to be placed on another actor to make them look like me and then inter-spliced a small amount of footage of me from the original film with the actor in prosthetics to resemble me in order to fool audiences in to believing I was in the film. There was an actress that was replaced with another actress in the film, but they simply cast another actor in that role with no prosthetics. Had they simply cast another actor to play the role of George McFly there would have been no criminal activity on the part of the producers and there would have been no lawsuit. Since they did not own my face nor make an financial agreement with me to use my facial features what they did was stealing something they did not own for personal again and therefor what they did was illegal and why there was a lawsuit and why there are rules in the Screen Actors Guild that make it so producers can never to this kind of thing again.
Probably the most negative aspect about it is that Bob Gale who was a co-producer and co-writer and one of the main architects of the illegal activity has decided that it serves him best to lie about what happened in order to justify partaking in something that led to the producer’s illegal activity. He has falsely stated that I asked the same amount of money that Michael J. Fox was getting. This statement by him is complete fabrication. He is doing this to take the focus off the fact that what he and his fellow producers did was illegal, by definition of the word. He does not want to face that fact. To skirt the issue Bob Gale has lied to millions of people on the Back to the Future DVD commentaries about how the negotiations were handled. I would not normally discuss this sort of thing, but people believe what he has stated as true. What people have to realize is that Bob Gale was involved with something that he and his fellow producers turned in to illegal activity. People who wonder about if what Bob Gale has said is true or not, should understand even if they liked “Back to the Future” it still means that a creator like Bob Gale who was a contributor to the illegal activity has motivation to create lies to detract the attention from his wrong doing. I wonder if Bob Gale were asked if he would help produce a film with the same specific illegal activity if he would say he would do it again. For one thing the new laws in SAG that my lawsuit helped to create would not allow an actor to be hired to fool audiences in to believing they are another performer with the use of prosthetics or otherwise. Still putting that specific questions to Bob Gale I wonder what he would answer. If he would answer that he would help to do something illegal again I hope people would understand the lack of integrity that would indicate on his part. I would hope he would answer that what he/they did was wrong, and illegal and if they had to make the film without me playing the role they would simply cast another actor in the role like they did with re-casting Claudia Wells with Elizabeth Shue as Jennifer character in the same film. In the very same film they re-cast an actress with a different actress, but they did not put prosthetics on Elizabeth Shue to make her look like Claudia Wells. For whatever what feels to me like being mean spirited, they decided it was good idea to put another actor in prosthetics and inter-splice a very small portion of me from the original film to fool audiences in to believing I was in it. There has not been another situation like this preceding it, and because of my lawsuit there has not been another time that another actor has been subjected to this particular sort of illegal activity. Again I am proud of the lawsuit and standing up against illegal activity that caused proper precedents and bylaws in to be set in the Screen Actors Guild. It is unfortunate that the producers of the Back to the Future films decided it was a good idea to perform an illegal action, which led to a lawsuit. In 2005-2007 I had a very positive experience working with Robert Zemeckis again playing Grendel in his “Beowulf.” When working together the subject of the lawsuit was never brought up. I am enjoying my life, making my films, touring with them, publishing my books and acting in other people’s films. If I were put in the exact same situation today I would react in the exact same way. Thank you for asking about it in that detailed way. I am glad to help clarify. People can find out about my films and shows and where I will be with them on CrispinGlover.com
I have noticed however that Bob Gale who was the co-writer and one of the producers on the films and one of the chief architects of the concepts that led to the law suit has been stating false things about me to attempt to lessen his wrongdoing. I do not like his false statements would like to remind that what he did caused laws in the screen actors guild to be changed to protect actors from his kind of wrong doing. I ended up having an excellent working relationship with Robert Zemeckis on Beowulf which was released in 2007. Despite the negative aspects of Bob Gale I am glad that I played the character in the original film.
You can troll the whole thing here.