Japan Creek is the perfect Japanese market. While they obviously can't carry everything, what they do carry is very valuable and more important than the other things. The prices ar reasonable when you understand it's a specialty shop in a good location, but if you are expecting Walmart pricing you'll be disappointed. Though if you're expecting Walmart, you probably can't appreciate a tiny Japanese market anyway... but it's never too late to branch out.
They also offer bento boxes and riceballs of various flavors (tuna mayo, go get it), and they're good! They bring in baked goods from Mammoth Bakery in LA, so there is even a hookup for Japanese pastries (curry-pan!).
It has truly made our experience living in the area better. We were worried moving to Las Vegas because of a small-ish Japanese population, but having Japan Creek near by has made us feel very comfortable.
The staff is always friendly and happy, but you may want to brush up on Japanese lessons before trying to chat.