Only been out there a couple of times but had a really good time on both trips. As others have said, the snow can be on and off. When we were out there in the late 90's, they had a 100" snowfall within a couple of days after we left. Honest to God.
On one trip we actually stayed at a working ranch not far from Flag Mountain Lookout. Rode across the pasture and on to the trail. On a previous trip we stayed at the Deadwood Gulch Resort. Great place - in-house casino and the best prime rib I've ever had. Deadwood is pretty cool. Highly recommend a stay there.
Riding can be very good. As far as I know, everything between the trail loops is open for off-trail riding. Great scenery and a lot of rolling meadows. Hope to go back someday.