I went to Happo-one on Jan 26 and had a great day. The snow wasn't the best, as it was a little bit warm (3 degrees) but there was still some good deeper pockets to be found in the trees.
I was surprised at how much larger the mountain was compared to the other Hakuba resorts. You could definitely spend a few days there without getting bored of the terrain. The runs were pretty long and the grooming was excellent.