I love 4DS, although at 36 weeks pregnant, I can't really do any of it.
I tend to use the premixes more than the series as is. I love the total upper body split, the Chest, shoulder triceps premix, the back biceps premix, the legs only premix, the premixes that combine cardios, and various weight/cardio circuits.
I think I'll be preoccupied with STS after the baby for a long while, so I'll just be using 4DS cardio, not the weight segments for some time.
I love the heavier weights and I think the cardio segments are really fun and complement each other well--the step segments are more complex and the kick box and boot camp are not complex, but will get your heart rate up.
The only thing I really didn't like about this series was that Cathe ignores the beat of the music during the weight segments at times and I wish she could have just made adjustments in the music or something. I like to stay on beat.
I think it's a great series.
Maggie