Whew! It's been years since I read that book, so my recall may be a bit faulty. My objection isn't that they want to give it the SciFi treatment (better than ya monster of the week: Bats, for instance; fercrissake!). But let's call a book the fruit and the adaptation a jam. How to best retain the flavor while boiling down the story and condensing the experience? Tricky. The psychodrama with Gully Foyle as Mr Fourmyle was, um, kind of weird even in the book. They'll need to keep the asteroid-dwelling primitives as a plot point, at least. Then there's the whole problem of Gully Foyle not being the most sympathetic character...
Hope it plays as well on screen as it did in my head.