Are you referring to easy to follow and learn? I haven't had trouble learning any of Cathe's kickbox (and I don't pick up things easily).
If you are talking about intensity, Kickmax has the slowest and easiest kicking and punching combinations--much less intense, in my opinion, than KPC or CardioKicks. BUT the intensity drills are another story. The leg conditioning drills are excellent.
KPC is my favorite. I like 4DS Kickbox. Cardio Kicks works my upper body the most. Kickmax is my least favorite, but it is great for the legs--and the heart.