I went to Marunuma Kogen 3 days in the 2009-2010 season. The first day was the last Saturday in November, when they only had 3 courses open (Yellow, Violet and Cobalt). While the snow was mostly artificial, it was not bad quality, and it was a nice sunny day. The line for the bottom lift was horrendous, but once we got up it we stuck to the upper lifts and didn't have much problem with lines. I went there via the Konsei Touge via Nikko and Chuzenji-ko, which was a scenic and traffic-free route. That road closes by late December though, and probably gets pretty hairy before that.
After that I managed to score a free giveaway ticket to Marunuma (thanks SJ and Marunuma!), and made a weekend of it in late February, staying at Pension Currants (listed on this site) Saturday night.
Saturday was sunny when we arrived, becoming snowy, windy and zero-visibility by the end of the afternoon. After a very pleasant stay at Pension Currants, Sunday turned out to be a spectacularly beautiful, blue-sky day. Not too cold, not too warm, no wind, squeaky packed powder, great views... just a perfect day.
It was busy, but not crowded. Parking lots were full, and restaurants were busy, but there weren't any serious lift lines anywhere; the longest wait was for the gondola, and that was only a few minutes. No real crowding on the slopes, either; they seemed more crowded when I went in November, probably because everyone was confined to 3 courses then.
They do seem to have a fair number of lifts scattered about the lower slopes, which I guess helps minimize choke points. Interestingly, even at that I did notice a fair amount of deactivated lift capacity. At least 4-5 lifts were in various stages of disuse/decommissioning -- I guess they aren't needed any more. Though one, Oohiro, was down just for the season for improvements to the trail it serves. (Unfortunate, as that trail gets good reviews on this site -- but I see it has since re-opened for the 2010-2011 season.) It would be nice if all the lifts were equipped with safety bars, not just the high-speed ones.
The resort is not too large but big enough, about on a par with most of the places I frequent in Fukushima and Tochigi. The nice thing about this place is that the terrain feels very three-dimensional, something which is not obvious from looking at the map. Each course is in its own little gulley, and skiing around it feels like exploring nooks and crannies, and there is a good variety of trails to keep one entertained. The view of Shiranesan from the top of the gondola is of course very photogenic, and the views of the mountains on the other side are somehow cozy, especially from the lower runs.
This resort charmed me quite a bit, and I would happily recommend it. The only unfortunate aspect for me is that for most of the season the back road via the Konsei Touge is closed, which means having to go there from the Numata side. I'm glad I was warned by others on this site about how bad traffic on the Kan-Etsu expressway could get; I left early on Sunday and minimized my exposure to it, but from the traffic reports on the radio it seemed I escaped by the skin of my teeth.