I like this club and the setup. I have been here a couple of times and it is a mixed bag of quality of comic that you will see but generally they are pretty good. The audience size varies greatly from one show to another. I have been there when it was packed and another time where there were 25 people there.
This venue is kind of hard to find if you don't know there is an upstairs which is probably the reason for the crowds being small at times. They really need to promote it more because of the poor location in the building.
If location on the strip isn't the reason you picked Riviera, you would be better off at Bally's comedy club.
http://www.rivierahotel.com/las-vegas-entertainment/comedy-club/