Not a particularly inspiring environment, besides the good beaches and view of the mountains. Non-existent developer community. Sufficiently sized city (200k) to have everything you need. Fun festivals.
For our family of two adults and a baby, our living cost is very roughly $3000 / month. Biggest cost is my health insurance, second highest expense is rent, our place is $720 / month. You need a car to survive.
At first it seemed that taxes would be much cheaper than Finland, but actually there are many varieties of fees and when you add them all up Japan is about the same. Putting a child through the schooling system would tip that in favor of Finland, where they actually pay you to study.
I wrote this ages ago, been meaning to update it: http://www.bemmu.com/what-it-costs-to-live-in-japan