Squats are the best. You can just ask my clients, I really really like them. Do you want to know why I like them so much? Because they work. Squats involve so many different muscle groups. They burn a lot of calories, and they will whip that butt into shape, literally. This circuit can be done without weights, but if it is seeming too easy add dumbbells to increase the intensity. 
If you keep up your tempo while you are squatting your heart rate should stay up! Be sure to keep you awesome squat form. Hips back like you are sitting in a chair, weight in your heels, knees stay in line with the ankles, avoiding pressing forward over the toes. Squats shouldn’t be hurting your knees if you are doing them right. Happy squatting peeps!
Whew, that sounds like a tough one!