I have it on good authority that this place serves some of the most authentic Thai food in the valley. Never having been to Thailand, I can't say - but what I can say is that I've been here many times, and the food and service never disappoint!
Royal Thai is in a small strip mall. Neither the exterior nor interior are anything special. But the food! It's a great place to go with a few friends, and order family style. But if you like it spicy, be sure to let them know - otherwise they tend toward less spice for American tastes.