Authentic Japanese is quite different from authentic Chinese. Chinese cuisine should ideally be about using herbs and spices to bring out the flavor in each dish. Japanese cuisine, well, tends to favor sweet and sour foods (the impression of that as Chinese is incorrect; only Cantonese food tastes sweet) & focuses a lot on the materials themselves and the preparation. In China, the design is very important -- believe it or not, good dishes have to look pleasing and have a "lucky" name.
Another difference is Japanese will eat raw food (esp. fish), and most Chinese hate anything raw, except maybe spices like garlic, ginger, and green onions.
I'm answering based on my own opinion of the two kinds -- I'm Chinese, so I've had a great deal of that. I also have tried many Japanese foods, having lived there for two years.