Last time I was in sin city I did a seafood buffet at one of the big places on the strip, may have even been Mandalay Bay. Ask the concierge for the best seafood buffet.
Normally if I ask for good eats and someone mentions "buffet" I just smirk and keep walking, but this one really was excellent with very good seafood.
Disclaimer: Last time in Vegas was about 15 years ago, so this may not even exist anymore.