Definitely a case of quantity over quality.
On the plus side, hundreds of thousands of roads that weren't there before have been added. On the minus side, major arterial roads, highways etc that had been mapped have been deleted, mashed up, sliced up etc. There is no consistency with road classifications either. As far as a navigation system for getting from A to B, the quality has dropped dramatically, certainly in my area at least. There is a mountain of work for editors to get it back to a usable level, and from my experience of customer service in Japan, I would not push it to a wider audience just yet as you will just end up scarring people off.
The address system also needs localisation. Addresses here are based on blocks, not streets. Like Prefecture>City>Ward>Town>Area>Block>Building or Prefecture>County>Town>Area>Building. National and Prefectural routes, Expressways etc are named and some streets have names too, but they are not used for addressing.
On the plus side as a semi-active Waze mapper, it's a points bonanza
One other point of note, and this applied before the mass edit, there are a lot of app users who map train lines because they are not shown on the app even though they are mapped as railways in the editor. Showing them on the app would save us the trouble of having to delete them all the time. One Japanese mapper has suggested marking them as boardwalks to avoid this problem.