I feel all the weight workouts with 4DS. When I've done the lower body (only two times so far) I've really felt it. I also love that she gives the calves a great workout too. But the reason I am so happy with this series is I just do not have more than an hour to work out and 4 days is pushing it a week for me. I am really enjoying the one body part per week rotation as well. It lets me go heavier and not feel useless the rest of the day.
But thankfully Cathe has so many options and workouts that we can all find something to make us work and keep up happy!