1) Like P90x, it is a three-phase program. The big key for me in X2 is there is more variety. For example, in P90x aside from the recovery week, you did the same legs and back workout every week. In X2, the only program you do in more than one month is the plyometrics workout. That is in phases I and II, but not in III. There is a recovery and mobility DVD that you can also use on your rest days throughout the program.
2) X2 yoga is much better. It takes all the good stuff from the original p90x yoga but compresses it into 61 min as opposed to 90 minutes. It flows much better, and I never found myself getting bored or wishing it would stop.
3) Foam rolling is awesome. In P90x you had a stretching DVD that you could use on your rest day. Here, there is a recovery and mobility DVD, the bulk of which is foam rolling. It is hard if you have never done it before, but if you stick with it, it will make your body feel so much better. The rest of recovery and mobility is stretching and low-impact movements.
4) There is less cardio in X2. X1 had the karate workout, plyometrics, and an optional cardio DVD. The only traditional cardio workout in X2 is plyometrics, and it is very different than the X1 version. The circuits in the regular workouts however kept my heart rate up so I still burned a lot of calories. And, in phase III you basically alternate two different workouts which do have quite a bit of cardio in them, and you do the 4 moves in the circuit back-to-back without stopping, then repeat the circuit 4 times. While it does not get your heart rate up like a program such as Insanity does, it does make you winded.
5) They focus a lot on the modifier in X2. They really set the workout up so you do not need all the equipment for people who are not ready to be balancing on medicine balls and stability balls, or who are traveling and cannot take all the equipment with them.
6) While some of the workouts are similar to what you saw in X1, they are more challenging. There are still lots of pull-ups and push-ups, but you are doing push-ups on medicine balls or stability balls, which are much different than they are on the floor. Even if you have done several rounds of P90x, there will be somewhat of a learning curve in X2.
Obviously, the best workout for you is the one you can stick with. I like rotating the beachbody workouts because, let's face it, the same workout over and over gets boring, and even when split into phases your body will begin to adapt. The price on Amazon is pretty steep (you can find it for a lot less), and you always have to watch out for bootlegged copies from third-party sellers. There is always some subjectivity in what you are going to like or dislike. For people who are fans of the original, I think X2 definitely will have something to offer.