Although I can't help you with sushi

Haven't had any luck in that department in Vegas.
-Gordon Ramsey Steak or Hell's Kitchen - either place, try all his fave dishes - beef wellington, scallops, risotto, or the best brown butter ice cream and sticky toffee pudding!
-if you want to break the bank, Joel Robuchon's restaurants have 1 or 3 michelin stars (in the MGM). Pricey french food, but if you're a foodie - you'd appreciate it.
-Momofuku - chef David Chang (Mind of a Chef) has the best noodle bowls! Around the corner there's Egg Slut - which have simple, yet tasty, egg based dishes.
-Fleur - more french cooking in Mandalay Bay. Excellent, and not as pricey as Robuchon.
Is it your first time in Vegas? If you've been before, where would you recommend?