I have taken the bus from Kingman to Las Vegas. Actually, it was very dark that night and I don't recall whether it was mountanous or not. However, on approaching Las Vegas and all the lights, it was quite spectacular.
The train to Kingman arrived late. There were two vans (they don't use buses) and the drivers pulled into a restaurant and had breakfast about half way to Las Vegas. A short break would have been nice, but it was late and none of the passengers really wanted to wait while they ate. I didn't get to my hotel until 5:30 a.m.
The ride was ok. Not as nice as the train, but it was ok.