Hi Rattle,
You might want to consider Hakuba, which is in Nagano. They had the winter olympics there back '98, so the snows sound as a pound and the mountains are excellent for get some speed up. The main ski area is Happo One, where they did the mens down hill.
Have been skiing in Europe for most of my life (20 years), but moved to Australia - Japan is easily the closest / best place for skiing from down here. Mountains may not have the extreme pitches that some European resorts have, but there's plenty to keep you entertained, even if you're a good skier/snowboarder. Food and culture are also top.
There's a lot of raving about the north island, more snow, but to be honest when one areas 11m and other is 12ms of annual snowfall I'd go with the one that's easier to get to. Hakuba's 3 hours from Tokyo, plus it's not awash with backpack Aussie types.
Stayed at a couple of places, but recommend the Double Black hotel, that's where I was last year.
Double Black Hotel | Ski and Snowboard Accommodation Hakuba Japan
Have fun mate, you'll love it.
Andy