Have to echo the first reviewer.
Simply the best. The 23rd floor sky lobby offers sweeping views of Las Vegas. There's someone to greet you when you get out of the car, one for the door, one for the elevator up, one when you get out of the elevator, and someone at the front desk.
Talk about feeling like a VIP, seriously. It's kind of ridiculous.
The lobby lounge is gorgeous, well appointed, and the views are killer. I mean, it's about what you'd expect out of the 12 billion dollar city center :)