"Kani Doraku" Osaka dotonbori is the most is a famous shop.
This restaurant also seems to be highly rated.
"Okudo san Koshiba"
Dancing Crab is a fun restaurant, especially if you are with kids!
This is the seafood restaurant where you do not use knives and folks, eat all food with hands! However, it's originally from Singapore so the taste is not exactly Japanese style.
Matsubatei seems to provide high-grade crabs.
Their food course is reasonable price, considering the quality of crab (all caught in Japan) and atmosphere. The restaurant is a reconstructed building of old Japanese style house, so you get to enjoy atmosphere of traditional tatami room.