I think that the real question would be "what does it mean to be on IMDB's list". I mean, what does it tell us? Which films are better, or which films are more popular? When someone states "this film should not be on the list" he's probably thinking of the first one - that this is a list of the best films of all time. But actually, it's probably the second that happens. So, can a movie be "overated" because it's popular? Many of us love some very bad films, but of course, films can become popular for various reasons (good marketing, for example) other than their true "artistic" merit. Point is, for a list of popularity, the term "overrated" has no actual meaning.