I personally feel that a CD can enhance a cruise but cannot ruin one. On a Royal Caribbean cruise last year I did not care for the cruise director but it by no means made the cruise less enjoyable. On the other hand, I have had CD's, Adrian Lewis on NCL, that greatly enhanced the cruise.
If you are on the cruise to be entertained then the CD will have more bearing on your enjoyment. If you are on the cruise to enjoy yourself then the CD will have less of an impact.