I agree with SKO about Picasso and Delmonico, and would add Aqua (at Bellagio), which has great service and the best food in town. Picasso has the best atmosphere of any restaurant anywhere but it has an extremely limited menu so it may not be the best choice for picky eaters.
I've eaten at Aureole twice and thought it was good but not world class. I much prefer Red Square (also at Mandalay Bay).
Isis (at Luxor) is a wonderful gourmet room with superb service and food. Olio (at MGM) is just wonderful under new executive chef Clay Conley, and don't forget Emeril's New Orleans Fish House, also at MGM.
Bon Appetit!