I went to City Center at the beginning of January. Pretty much stayed around the area, just to get to know it. It is a pain with a car. But as far as dining, I enjoyed a meal early evening before it became a night club at the restaurant by the Desperate Housewife chick Eva Longoria outside the shopping area. (the crab cake, soups and sauces for steaks and fish were good)
At Aria, I dined at Julian Serrano and it was a bunch of small, tapas plates for lunch. I ate many items but remember liking the Spanish Chicken Croquetas and Creamy Risotto. The menu was endless!
Another meal was at Jean Georges Steakhouse for dinner, (steaks were very good, and calamari was a great appetizer) Although I think I would have rather gone to Maestro's.
American Fish was excellent, Grilled, Poached or Baked fish, Michael Mina could do no wrong. It was also nice that it wasn't too busy.
I also loved the Lemongrass Thai food for a casual lunch. There were five of us, and we all ordered different items and shared everything. Very tasty. (I think mine was a spicy prawn dish, but everyone's was great. We let the waitress choose a few too.
Overall, each of the restaurants at CityCenter were good. I have dined at a lot (A LOT) of places in Las Vegas and haven't always enjoyed every dining experience. I couldn't complain about any of them at the City Center. (oh and I was with a bunch of foodies and they liked all the restaurants too)
I am sorry, I should have added that the art work and fountains are amazing and impressive. If you can, get a little brochure from a concierge about the art and fountains and wander around to find the various pieces. I went home and looked up info about the artists online, but wished while I was there the brochures had more info about them. Fountains are also included in the shopping area. It was pretty quiet there. I didn't get a spa treatment and was annoyed that I wasn't able to see inside Aria's spa. (as a guest - you would think) So if you have the time, get a treatment, I hear the place is nice (I personally love Caesar's and the Mirage).