Full Disclosure: Teih'anda Horieten is as close as I've ever come to Okinawan food. I was not able to make it to Okinawa in the year I spent living in Osaka. That said, this restaurant is routinely ranked among the best in the country outside of Okinawa.
Okinawa is often compared favorably to Hawaii. Fresh fish and produce, and the use of spam aside, Okinawans are renowned for their mellowness. It's easy to be mellow when your island has the largest percentage of centenarians per capita in the world though, right?
The food here is excellent. Absolutely can't go wrong with anything on the menu in my experience. I recommend the くぶいりちゃ (kubuiricha: konbu seaweed, shiitake mushrooms and daikon), the いかそめん (ika somen: squid noodles), and the fresh plate of Okinawan-caught sashimi. And make sure you try the quintessential Okinawan comfort food dish ごやちゃんぷる (goya chanpuru: sauteed bitter melon, tofu and spam).