Red Square IS a fantastic , restaurant, but it is not authentic Russian food.
The ambiance is beautiful. It is dark with red lighting that gave me the feel of Russian clubs/swanky restaurants from movies. The service is in impeccable. My wife and I were seated promptly, then greeted by our server (Melissa) within minutes of sitting down. Melissa was very knowledgeable of the drink and food menu. She was honest with her opinions of the food she liked and disliked and gave both of us good drink recommendations. The menu was amazing and my wife and I both ordered the tasting menu. Each course on the tasting menu had 3 options to choose from. After making our order the courses came out very well timed and Melissa was always available.
For two people with the tasting menu and drinks you can expect a high bill, but it is well worth it. This is a restaurant that I would frequent often if I lived in Las Vegas.