So this one is a bit frustrating! First, the good: the images themsevles are great. The National Archive of Japan seems to have spared no expense creating high quality jpeg and jpeg2000 images of maps, drawings, paintings, maps, etc. that can be zoomed in to your heart's content. The problem lies in the presentation, and the additional information and metadata provided (or in this case, not provided).
The home page of the archive gives you three choices for searching and browsing: a flash map of Japan with clickable provinces, a 'search by category' feature, and an alphabetical listing. Going by the map or the alphabet can be sort of disorienting: both lump materials of all sorts together. This isn't as bad for the province map (it's particularly useful, in fact, for finding... maps, of certain regions, as you might expect), but since the alphabetical listing is by title (rather than creator or artist) it's almost useless unliss you know exactly what you're looking for or browsing purely for discovery purposes.
Very little metadata is provided for each image. An informational blurb is attached to each, but there's little standardization of detail given other than date of creation. Searching through categories makes things a bit better, since you can then search through individual collections of drawings and photographs with additional information (even artist biographys!), but this is somewhat hidden withen the interface. And even then, the metadata itself is contained within a blurb, rather than with the image.
Ultimately, there's a lot here that's interesting for Japanese Historians and Art Historians in general, but the presentation is lacking. Providing more metadata along with individual images would be an excellent first step towards improving the site.