I just returned from 2 weeks of fantastic dining in Japan. Thanks to SkylineR33, RobbS, Yukari, and Wandering Foodie—plus some hints from the Michelin Guide—I went to some really top-notch restaurants, as well as many lesser known, but very good ones.
I just saw exilekiss's photos and review on Ryugin and I think that it pretty much conveys how absolutely wonderful that place is. (Good job exilekiss!!) On my scale of 1 - 10, it got a 10. My only other 10 experience was Fukamachi Tempura. Yes, I know there's no way to compare a haute cuisine restaurant with a tempura one. But, among tempura restaurants, Fukamachi is superb.
Here are some others I experienced, in order of excellence:
Fukudaya and Kikunoi (both 9)
Ten Ichi Tempura (8)
Kushikura Yakitori and L'Osier (both 7)
Joel Robuchon (3)
Hamadaya & Yotaro Tempura (both 2)
I wouldn't go back to those with a 5 and under.
I have reviewed these all in detail on my website, but thought you might be interested in this summary