Overview: Yellowtail is a Japanese restaurant for people who are afraid of Japanese food.
When my wife and I went to Vegas for our anniversary, Yellowtail at Bellagio very nearly ruined it. For background: My mother is Japanese, and I've been fortunate enough to visit many times. I don't need my Japanese food to be authentic, but it does have to taste good.
Yellowtail's food is neither authentic nor good. The glazed salmon I ordered was soaked in a sugar sauce, sweet to the point of being inedible. (My theory: To cover up the fact they serve cheap salmon.)
To their credit, when my waiter came over, he immediately asked me what was wrong. When I told him, he quickly replaced the dish with something edible but completely forgettable. (The good service is the only thing that brings Yellowtail up to two stars.) My wife had a similar experience. The food is more "Japanese-y" than Japanese.
Unfortunately for me, I had a severe stomach ache for the rest of the night - a distraction to say the least when I was trying to enjoy Cirque du Solei. The Bellagio hotel staff were completely unhelpful to the point of belligerence, but that's a story for another time.
My wife and I are already planning our next trip to Vegas. We would have considered staying at the Bellagio. But after our experience with Yellowtail (and Bellagio), we're going back to the Wynn. They certainly know how to treat customers well there.