Mix is fantastic. The best dining experience we had this trip to Vegas was at Mix by far. The service was fantastic, our waiter was attentive, quick and didn't mind a little chat since it was a little slower the night we went. The food was amazing, really tasty, perfect portion size, and not too slow. The view was spectacular. Ask for the balcony/patio if you can, you won't regret it.
I only had one minor quibble. We were dining on Halloween and I emailed the restaurant to ask if it would be alright if we showed up in costume. They indicated that would not be allowed so we arranged to get dressed up after dinner instead. When we got there, tons of people in costume were in the restaurant. That was disappointing.
Overall, I would go back in a second.