High end books, medium rare & antiquarian books. Nothing junky.
Wide selection -- bigger than Charles Parkhurst, smaller than the Book Gallery. Specifically, there are nice sections on Asia and the West and an amazing (and amazingly high-priced) selection of science and medicine papers (reprints) and journals.
For unique items that no other bookseller has, the prices are not unreasonably high. But for items that are more widely available on the internet, his prices are often higher than the internet price.