I think Chris Rock was just a little out of his league last week. He seemed at times to be a bit bewildered at the intelligence of the other guests. On top of that he appeared to be a bit hungover or something. I think the show would have been much better if he hadn't shown up and they had just been short a guest.
They have some clips from the monologues and New Rules on the HBO site:
http://www.hbo.com/billmaher/video/