If you consider yourself intermediate to advanced, you should have no problem with most of Cathe's workouts. I considered myself between beginner and intermediate and my first Cathe workout was Step Blast. Wow! It was great! It took me a few times to really get it, because my endurance wasn't built up, yet. Otherwise, I had the footwork down pretty quickly. Once my lungs caught up with the rest of my body, I was flying through this workout in no time!
If you are looking for pure step, I'd suggest Step Blast, Rhythmic Step, or Lowmax (the DVD has a fantastic all-step premix). If you are looking for super-intensity, I'd recommend one of the Imax's (maybe not Imax 3, yet, though -- it's pretty advanced, IMO, and the footwork is some of Cathe's most complex she's ever done).