This is the best Thai restaurant that I've experienced. Because of this it is a famous "must visit" dining destination for Las Vegas visitors. When I have business in Vegas, I always plan an outing to Lotus of Siam.
Don't come here and order typical Thai dishes like Pad Thai, Panang and Drunken Noodles unless you jazz it up with something like crispy duck. Order from the Northern Specialties since that is the most special part of their menu and arguably what they are best at.
Khao Soi, another comfort food dish with noodles and meat in a panang curry like soup with pickled vegetables and raw red onions is delicious and a go-to dish for me.
Nam Kao Tod (a puffed crispy rice salad with preserved sour pork sausage) has volumes of flavor (spicy, sour, minty) if you're looking for something different.
Try Nam Prik (a composed room temperature chili based salad), Jackfruit salad, Hung Lay (pork curry braised down with garlic and ginger), Northern Larb (their version of comfort food).
The garlic prawns are a crowd pleaser and a safe choice for non-adventurous diners. The Drunken Noodles with crispy duck is another crowd pleaser.