Montana is a VERY big state. The KOA in West Glacier is very nice indeed, and has some mountain view. Mountain view perhaps more spectacular from the KOA in St. Mary, on the east side of Glacier, but the CG isn't quite as nice. (It's fine, especially as a base camp for sightseeing.) Grizzly is great too, but there's not much mountain view from there, just the Yellowstone plateau.
We haven't been, but you might check into some of the CGs south of Livingston, in Paradise Valley. That's a beautiful area.