For an old Vegas feel and a meal made to feed you like a king, this is one place that I highly recommend. The food quality and portioning is fantastic! I always tell my friends to get to this joint for breakfast when they come to town and get wasted on the Vegas Strip (after sleeping it off in their hotels) because there is nothing like a big breakfast to make you feel human again. I should also say that this is located south of Vegas in Henderson, but it is well worth the jaunt.
There are so many things on the menu that I really can't narrow it down to one that you must absolutely have, but if you're coming for dinner, I would highly suggest the prime rib. This is the stuff of legends and is known all over town for it, trust me. Matter of fact, this was what sold me on trying the Rainbow in the first place. The prices will have you reeling because you will not believe how cheap it is to eat so much food.
They have an awesome high definition tv system with world wonders always playing and it is their "art" which is cool. You will have to deal with smoke-smell because it is allowed in the casino. The waitstaff are very good -- they deal with the nicest people to the worst drunkards all day, everyday. The absolute only thing that I'm hitting them on is their hours. They are not 24/7, which is a darn shame. Otherwise, please spend your money here and tell your friends!