I love mountain biking, What do you think about it?
I really enjoy it!  I especially like to ride on mountain trails, singletrack, fire roads, and other unpaved surfaces.
Riding on the trails is great, Mountain bikes were in fact pioneered by Americans to be recreational. 
Trail riding is fun!  I like to ride on  trails, bridle paths, and forest roads, but not on roads regularly used by motorised traffic.