I had been to the Rio World Buffet more than ten years ago, and either my food palette has changed radically in that amount of time, or this place has dipped in quality. Possibly a combination of both. In any event, I was sorely disappointed. The food was mediocre at best. The prime rib was very salty, the sushi barely qualified as sushi, and there were more fried, breaded offerings than you can shake a one dollar bill at. Highlights were the cheesecake (you might have to ask the dessert attendant) and the har gow. Go figure.
If you're looking for a great value, there are probably plenty of mass quantity dining options in Vegas that are just as good.