The past two times I visited Vegas, we hit the champagne brunch (Sat & Sun) and were not disappointed.
First off, the room the buffet is in is just really NICE. It's decorated to resemble a turn of the century train station and is very pretty. Definitely feels nicer than the $13 or whatever the insanely low price is for the champagne brunch.
Secondly, both times we've had amazing service. Your drink never empties, and that includes your champagne. If you come to a champagne brunch looking to get loaded this is definitely your place.
The food here is pretty good. There is a massive selection for the brunch, with Chinese, Mexican, soul food, standard American stuff, standard breakfast stuff, and a big salad bar. We thought it was all really fresh and well-made.
Bonus: if you look online you can probably find a 2-for-1 coupon! You just have to be a member of the player's club.