I've read almost all of Arthur C. Clarke's novels. The Rama sequels are nothing like his work. It's easy to believe that he barely contributed.

I always felt that Gentry Lee kidnapped Clarke and forced him to be his co-author.

Clarke was so much of a better writer than the [2010|Rama] sequels indicate. He would not be able to screw it up so thoroughly without extensive "help".

Clarke also made some good partnerships - Richter 10 is a very good book. Sadly, the partner died and never worked with Clarke again. Gentry Lee would be my main suspect.