Well, I am spoiled, because I live high in the mountains of Colorado with a half dozen world class resorts minutes from my door.
However, there are definitely good resorts for snowboarding in Japan.
My advice is to avoid weekends and holidays at all costs, especially on the main island of Honshu.
I would expect and have heard that Hokkaido has less of a problem with crowds, but like anywhere in the world, weekdays are still likely to be better than weekends.
There are a lot of people in Japan if you haven't heard, and a whole lot of them like to ski and snowboard. Sliding down as one small speck in a giant moving human carpet is only amusing for about 30 seconds. Then it becomes a rather unpleasant ordeal.
The luxury of America is the sheer size and relatively small amounts of people packed into that size. Even on a weekend here in Colorado, with 20,000+ acres of lift serviced terrain at the resorts in my neighborhood, the tourists can't carpet the terrain.
In Japan, they can and do carpet the terrain often, especially at resorts that are close enough to Tokyo for weekend getaways.
Still, there is fun to be had snowboarding there. I plan to snowboard again in Japan, but I am looking forward to Hokkaido more than Honshu, and I will be planning on weekday excursions.
Dan Savage
Savage Snow Website