I had read it a couple years ago and decided to reread it about a month ago. The first time I read it I found it a little hard to stay focused toward the end (don't want to post any spoilers, im sure you can guess what was a little hard to keep my attention.) and I was 15! This time around it was easier. If your 9 year old finds it interesting, my hat goes off to him.
Have you read 2010? Its not as good but it ties up the story of Discovery and whatever happened to HAL and Bowman. Im rereading that now.