Sci-fi and blockbusters rank high on my list of movies to avoid, but with "Back to the Future" showing for months at the AMC Fiesta Village I worked at in high school, it was hard not to get swept up in this one. (A seems-funny-now crush on Michael J. Fox didn't hurt, either.) Hard to believe it would take 25 years to find out that Eric Stolz was originally cast as Marty McFly, but was replaced by the "Family Ties" star after five weeks of filming left director Robert Zemeckis felt "something was missing." (I was never a huge fan of Stolz, either, although I would end up loving him in the short-lived Showtime series "Out of Order.") This is one of the biggest big screen replacements that I can recall -- a smaller one was Woody Allen's revolving cast of "September" -- can you think of any bigger ones?