I just don't see it as one of the all-time greats. Like the poll indicated, Gump won best picture that year, and I'd consider Gump a superior movie as well. But like I stated, all lists are subjective, and to each his own. Great flick, but greatest ever? Not to me.
To even pick a "greatest movie ever" is a daunting task IMHO, and it'd really depend on your taste/age. Breaking it down by genre would probably be the way to go.