Tried Shake Shack for the first time in Las Vegas over the weekend. There was a line out the door but it moved fast and everyone seemed to be in good spirits. They have 4 or 5 cash registers which really speeds the process up.
As for the food, we enjoyed the SmokeShack burger and the cheese fried were amazing. The malt shake was just okay, almost like a soft serve ice cream shake. We like a more texturized milk shake like at McDonald's.
Service was great, plenty of seating, and don't be afraid of the long line because it moves fast.