I've been to Onikoube fours times so far in the 2010 season and the conditions varied each time. The first time was decent with a nice amount of snow and only intermittent ice patches. The second time was extremely snowy and had frequent whiteouts. The third and fourth time was very icy, which meant pain during every fall.
The resort itself is on the small side, but it's cheap and a one day pass comes with a 1,000 yen food voucher which pretty much covers lunch. The courses are few, but the top of the mountain has a few fun trails and there are opportunities to go off course and into the trees.
In the end, if it's a distance away from where you live, I'd say you might as well invest the time to go somewhere better (Getou, Zao and Appi come to mind) but if you're a local (say, 1 hour drive or so), then it's a nice place to visit.
Snow condition on visit:
Light on a couple of occasions, but very icy on others.