Prices - ridiculously high ($18-20/cocktail, $9/miller lite)
View - best ever. Seriously, I used to go to Mandalay Bay's Foundation Room regularly and their view is about half as good as Mandarin Bar's.
Ambiance - this is the most swanky I have ever felt walking into a place in Vegas (or anywhere else for that matter). There is a dj, so there's music going on, but the place is pretty much always quiet. Never a problem finding a place to sit at the bar or one of the small tables along the amazing windows. Even just driving up to the Mandarin you feel cool because it's secluded from the rest of the strip. I love how they did that.
Cocktails - delicious. The specialty drinks on the menu are awesome, or just tell Mike what you want and he will mix you up something to suit your tastes.
Service - excellent. Just what you'd expect when you are paying these kinds of prices. There's about 1 staff member to every 5 patrons (or more, depending on the night), so they keep your drinks and snack trays promptly filled, but don't bother you otherwise.
One extra bonus: on Mondays (or maybe Tuesdays - I forget), they usually have some kind of featured drink or featured alcohol (once it was like a tea sangria and once it was some kind of vodka). Featured drinks are far far cheaper and sometimes you can even get free refills!