Oyster sauce is YUM. Its pretty salty, other than that I'm not sure how to describe it. We make a delishious steak sauce with it. Our local grocery actually carries it in the Asian food aisle, near the soy sauce, etc.
It is definitely available at my store, but I wondered if it was worth taking up more space when I already have fish sauce, soy sauce, sesame oil, and a million other Asian condiments. I seriously think oyster sauce is one of the only things I do not have!