It's a little difficult to verbalize but I'll try. Most of the time I ride for utilitarian reasons -- going to work, picking up books at the library, getting groceries, that sort of stuff. It's fun but my focus is really on getting to my destination safely, and I spend most of my mental energy monitoring traffic and road conditions. Besides that, I don't really have a lot of confidence in the ability of the bike to handle whatever obstacles the road may throw at it. But on the mountain bike, all that changed. Once I got off the road I was free to simply experience the ride itself. And they were expensive full-suspension bikes that felt as if they could roll over just about anything. I did things that I'd be very hesitant to do on my normal bikes, and it was like being a kid, playing with the bike for the pure joy of it, being free to explore places a road bike couldn't go. Riding in the dirt was exhilarating too -- suddenly sliding around didn't signal impending disaster, and the feel of it under my wheels was so different from pavement, so much more varied and nuanced. I love the sensory richness of riding, the sense of being immersed in the elements, and the mountain bike intensified that.