I've been to most of the well-known Japanese restaurant establishments in the area, and I only found one that I can truly recommend as an authentic, Yao-Kiku. I've developed a keen sense for Japanese cuisine from living in Japan for 15 years and at Yao-Kiku that's exactly what I get. The atmosphere is always relaxed and you can enjoy your meal without distractions. As John Ash states, this really is the "Best Japanese Cuisine in Sonoma County."
Pros: great food, great atmosphere, ample parking
Cons: can be crowded