[Nyororin]

Christmas isn`t a real holiday in Japan, and is only sparsely celebrated - so pretty much nothing closes. New Years, on the other hand, is closer in feeling to Christmas/Thanksgiving. Everyone heads to the relatives, and most places close over the New Year holidays. Chains will be open, I imagine, but smaller places will likely not be.

It is going to be hard to really hit on somewhere awful unless you`re looking for it. Japan has fairly high standards for restaurants to begin with. If the place looks run down and has no customers - either they`ve gone out of business or are about to. Places that are good will be fairly obvious, with lines, many customers, etc.