Restaurant Sakura is an traditional Japanese restaurant in a non-traditional setting. Inspired by an actual, historic restaurant in New York City, Restaurant Sakura is supposed to have been a fish market in its previous life. The fish market look-and-feel are still there, but make no mistake, this is an upscale, table-service Japanese restaurant—sans tatami mats.
The food is wonderful, provided you like Japanese of course. (Note that this is mainstream Japanese, so you won't find fugu or anything else terribly exotic.) Although the prices are on the higher end, they compare favorably with Japanese restaurants you might find around Tokyo.
You'd think Japanese people would rather eat something besides Japanese food when visiting an American-themed entertainment area, but apparently that's not the case as the waiting list here tends to be lengthy, especially during peak hours. The most popular restaurants in DisneySea have what is known as "priority seating," which is basically a reservation system similar to the FastPass system for attractions. If you want to eat here, go early and get a priority seating reservation.