We had a corner seat on the edge of the outdoor cafe. This is one of the best people watching spots in Boston. Street performers gather here around Faneuil Hall and it makes for a great environment.
Don't expect the best meal you can have in Boston. For both a great meal and a nice outdoor spot I'd choose McCormick and Schmicks instead; it's just on the other side of Faneuil Hall. I found the meal to be much better and the location and outdoor cafe just as good.
At Plaza III, you may enjoy the crème brulee covered in fresh strawberries as it was definitely the best part of the meal! If you're just looking for a spot to rest your feet and enjoy a good cup of coffee and dessert, this is it! For a full meal, I'd go elsewhere.