Libertine Social is a solid restaurant from Shawn McClain. We attended before a concert at Mandalay Bay and it was a good choice.
Make a reservation and be sure they honor it... In general I recommend Open Table reservations for all restaurants in Vegas because it's so easy to use and get (and never worth waiting when there are so many restaurant options in town). Be careful that they honor your reservation, when we attended they attempted to put us at a bar. The hostess seating us (different from the one that greeted us) let us know that their dining room was fully committed and that the bar was all they had. We know it was committed, we had a reservation, right? When we highlighted this, we were fairly quickly given a table but certainly not at the greeting hostess' delight.
What really matters, the food: The burger was very good, just be prepared for a two patty burger that is very filling. The Lobster Ravioli was one of the best I've seen in Vegas. Expensive but made up for it with lots of lobster. The filling was primarily lobster and corn. The "Black and Tan" pudding was dark chocolate and butterscotch. The butterscotch was amazing, the dark chocolate just okay. Overall a worthy visit.
Ordered:
Off the Menu Burger
Lobster Ravioli
"Black and Tan" Pudding
Overall: Good choice before a event at Mandalay Bay