SO and I went last week for my birthday. I had briefly considered cancelling the reservation based on all the awful reviews of their service, but we were pleasantly surprised!
Service: A- A+. The server was friendly, joked around easily, knew when to butt out, went out of his way for my birthday, etc. Spectacular, actually.
Atmosphere: B. Incredibly loud, but that calmed down as the night went on. I got the impression that that might well be an NYC thing, not a specifically Prime thing.
Appetizers: B- B+. The Southern chicken app that my SO ordered was great, but for 25 bucks, I want more sashimi in my sashimi salad. Tasted good though.
Main course: A. Solid steak dinner. Prices are astronomical, but we expected that. Split a steak and enjoyed very yummy mashed potatoes (esp. enjoyed the creaminess considering there's no cream) and artichokes (my first time eating them and WOW they were good)
Dessert: A. I ordered the cheesecake, and was completely floored when I remembered it had to be pareve.