I just had a "nice" ride tonight. Nice people, relaxed pace, nice time.
I'm not so sure about mountain biking being nice. At its best, it should be about fire in your belly, blood pounding in your head, and a dance through the trail. Or, it should be about epic places and worn out legs pushing worn out tyres around on a trail that goes to the horizon.
But nice seems like a hobby, not a passion. Nice has its place, but doesn't scratch the itch.