I had the same problem as JULSCARVER--I didn't feel it. I really enjoyed it, it was a fun workout, but it felt more intermediate level. I did use the same weights as Cathe so I will go heavier next time, but my concern with that is how fast the workout moves. It would be hard to go "heavy." I'm thinking I might try it with a weighted vest and 10 poun dumbbells. I didn't feel (at least with the 8 pound weights) it qualified as a cardio workout either.
I will say I felt it in my quads when we got to the standing chair work with the dumbbell held on the quad--that was painful for me. So was the floor work with the firewalker--that was pretty intense, too. I used a green firewalker for everything in this workout. In the future I think I will use the blue firewalker for the first/standing part but stick with the green firewalker for the mat work.
I really enjoyed the core work, too.