I have experienced it several times that people tend to expect "Picnic at Hanging Rock" to unfold like a detective story, while it is not one, in any respect. This movie belongs to another type, to the mystery genre, and possibly stands as the finest example of a film of this kind. The main purpose of such films is to contemplate The Unknown and Peter Weir copes with that excellently. What counts most here is the atmosphere, and the focus is more on hidden emotions than on the pacing (some say that the problem with "Picnic" is that it's boring - i don't think so but I guess it depends much on your sensitivity and approach). Most fascinating thing here is possibly the way the Rock is depicted - it appears as self-conscious entity, alive in a sense which is beyond Western logic. This, I think, is the key aspect of the story, because what it really is about is the conflict between the Culture and the Nature. And don't let this put you off as 'too philosophical'. Picnic at Hanging Rock, while not being a crime story, can be involving as one - if you help this to happen, of course. If you do, you might have a lot to think about when the credits start to roll. It can happen, though, that you will be dying to see them roll - there are no movies that appeal to all of us. Then, at least, you could enjoy the set design, photography and ancient beauty of wild Australia.
Give it a try. It's worth it. 8/10