I'm having trouble separating Vegas from Yellowtail, but I'll try my best...
The food and ambiance were nice, the service was just eh. We started with some sparkling sake with blueberry puree. It was actually really good, seemed like an odd combination at first, but clearly they know more about these things than I do because it worked quite well. The sweet chili sauce on the edamame was all very good. The sushi wasn't anything special. It was good, but nothing I'd go out of my way for.
The dining room was very pretty and the ambiance was nice. It's Vegas, if they can't make you comfortable in a restaurant then you're in the wrong place. Considering the prices you're paying I expect a comfortable dining experience. Overlooking the Bellagio fount is a nice addition to a dinner. I have a hard time calling anything in Vegas "romantic" but I suppose this should be deemed a romantic restaurant.
Seems like the place was crawling with staff, every direction you look there's a server or hostess descending on you. It was a little on the annoying side, but the food and drinks made up for it.
Overall, it was pretty good. If you're looking for good sushi on the strip Yellowtail is a good place to start your search.