I've tried many Thai restaurants in Seattle and this is by far the most authentic. The food is always great and served by a staff that treats you like family. The desserts are unlike anything I've had, make sure you try the Young Coconut ice cream with flan that arrives looking like a piece of artwork.
One warning, it's a bit hotter than most Thai restaurants, so you might want to take it down a star. Or just deal with the heat because this is what real Thai food is like.