This is the nicest looking Dim Sum restaurant in all of Vegas. It also provides the best service (I've read a few other reviews that say otherwise) but I have no complaints.
The waiters even come by to serve you tea. This is unheard of at Dim Sum's. You don't even need to do jumping jacks to get their attention to refill the tea because they will on top of it.
Since it's located inside Rio across from the Carnival buffet, the prices are a tad bit more expensive than your Spring Mtn options but it's still super cheap unless you are just a cheap ass AzN. All of the dim sum is really fresh, hot, and delish.
I recommend going super early to avoid the traffic and to get the food right when it comes out. I've been here about 5 times since it opened.