These are my impressions after using P90X. At this time I blend both P90X and Cathe.
Strength- as intense as you make them. P90X is a well designed gym style strength workout series with some weight work and some body resistance exercises. Difficulty will depend on how new some of theses exercises are for you and what shape you are in. I have done many of these exercises before so, I didn't get the DOMS or drastic changes that some people experienced. There are modifications for exercises and equipment.
*chest & back, shoulders & arms, back & biceps, and chest, shoulders, triceps (these are broken down like existing Cathe workouts)- rep speed is on your own most of the time so, it is easier to go heavy.
*legs and back- lost muscle tone. Substituted Cathe's leg workout for better results and killer DOMS.
*ARX- tough abdominal workout but got bored with the same old same old. Substituted Cathe's abd for variety.
*core synergistics- I like this workout. It adds functional fitness and strength. Since I use this in my regular rotation, I will sub in TLP videos on my rest weeks.
*yoga x- this one peaked my interest in yoga but 90 minutes is too long. Looking for a sub, any suggestions?
*stretch x- thorough stretch. I break it up because I've run out of days in the week.
Cardio- for me Cathe is more intense (so is Christi, Janis & many others).
*plyo x- I felt that during plyo x I needed to hit the pause button just to let the video participants catch their breath. Get a better workout from Cathe. I sub in the IMAX's.
*cardio x- as someone on another board said... where's the cardio.
*kenpo- I like this one but since this series lacks enough cardio for me, I use KPC.
P90X cardio was not a good match for me. Still good workouts. These are probably meant to save on muscle breakdown.
I agree with the people that say they'll never need another series. However, I will add from Tony Horton at the end of that statement. I sub for too many workouts from this series to buy another.
If Cathe's hardcore gym style workouts are at a slower speed, these workouts will be used for muscle confusion. I think they compliment each other. I don't experience any fun factor with P90X alone. I add Cathe for intensity and fun.
I would say buy them if they interest you, you want some variety, and you want to spend the money. If you really like Cathe and want to save money, wait for the hardcore series. You might get what you need from Cathe. P90X isn't going anywhere. Or compromise and buy a few.
JMO