If you haven't already, read the restaurant thread:
Vegad Restaurants .
I was there for a first time trip a few weeks ago and ate at Delmonico at Venetian, Michael Mina at Bellagio, and Nobu at Hard Rock. Nobu was my favourite: fantastic food and excellent service. I highly recommend going for the chef's tasting menu (omakase). The dishes flowed beautifully into each other, with a great variety of flavours. Delmonico was great, with top notch service as well. The only problem there was that I can only enjoy the first 12 oz of a steak, then I just keep eating out of stubbornness. Michael Mina was uneven. I had a seasonal tasting menu there as well, and had some very good fish as well as some rather mediocre fish -- not bad, mind you, just a little disappointing for the price. My waiter was also rather awkward and seemed mildly retarded.