Why do some 1½ hour movies seem so long, while some 2½ hour movies zip by so fast?

[Bucky]

I noticed this re-watching "I Am Legend," which was fun but seemed to get very little action done before they got into the final action sequence. Yet there are other movies that run the standard 100 minutes or less, but manage to cover a lot more narrative ground?

If anything, it seems like older movies used to get a lot more done with a much shorter run time.

[book_worm]

1. depends on the story and the director--can they keep it flowing and interesting

and yes, some long films can be bores because the filmmaker thinks it is an epic if it's long so they create scenes which have slow the film/story down (there are exceptions, of course). On the other hand many directors and writers have believed that a good story can be told in 90 minutes.