Everything! From the coaches pushing you in every part of the workout to the most effective workouts I've ever been through. Each day is different, and OTF keeps you on your toes, and I come home sore almost every time.
I like the variety in the workouts, and not knowing what to expect. I get bored with the same old routine, so it's encouraging to have the switch up. Also, I enjoy having a coach there to keep me accountable :)