I was in SF on business and the Hog Island happened to be near my hotel. Even though the Ferry Building is filled with tourists, and maybe the Hog Island was as well, I thoroughly enjoyed the experience of eating there. I had the clam chowder (filled with clams still in the shell) and a dozen mixed oysters, along with a few glasses of wine. It was so good, I had the same thing a few nights later!
The first night I sat at the counter across from two guys shucking oysters with the ease and expertise of professionals, which added to the fun.
There is indoor and outdoor seating along with about a half dozen seats along the counter. While there was a line both times, it moves quickly (and if you are alone, you'll usually get seated even faster as long as you're happy with the counter). The service is friendly and brisk and the view of the bay is an added bonus.
Will definitely be back the next time I'm in SF.