I do spin classes on occasion just for variety. They can be pretty goofy, but you can modify the exercises to your own ends (cadence drills, intervals, etc.) and of course you can turn the resistance up as high as you desire. I sit toward the back corner so as not to be a distraction if I chose to deviate from what the instructor is doing. I also usually wear earplugs to attenuate the too loud music and the instructor's inane exhortations and shrieks of encouragement.