I took my first of four spinning classes with almost a dozen other cyclists. It was my first time spinning seriously with an instructor. Each class is an hour long and includes intervals, sprints, hill climbing, and a few 60% pedaling rests.
I found it very realistic in imitating the climbs and descents of a real ride. Increasing the resistance and standing on the pedals really worked the quads. I really want to learn how to spin efficiently again. I still feel I am spinning a square rather than a circle.