The Rio Seafood Buffet, is a bit pricey. The out of town-er price for the buffet is in the mid $40's per person, but if you show your Nevada ID, and your players card they knock 10 to $15 off the ticket. It is not part of their Carnival World buffet, and is located on the east side of the main casino.
If you're a hot snow crab fan, you'll really enjoy the meal. The snow crab are large and abundant. They go through so many that they are always fresh out of the steamer. They also have oysters, clams, and a lot of what you would expect at a seafood buffet (both cold and hot), but the other items were low on flavor. They had an Asian style lobster dish composed of very small lobsters tails, and small shrimp, but this tasted a bit heavy and also lacking in flavor. The deserts were good and there was a wide variety.
I don't know if I would be a returned customer.