I bought the Master series after completing P90X by Tony Horton.
As I was nearing the end of that grueling program, I wanted something that would help me maintain my condition without having to keep up the P90X intensity all the time.
I actually also have the Original Power 90 programs and Tony Horton's Power Half Hour as well. While they are all great programs, my favorite one's to work with are the Master Series.
One of the things I love most about Tony's workouts is that they are simple to follow, no difficult choreography. For someone like myself, who doesn't want to have to memorize long movement patterns, this is perfect!
In general, I just want to be able to concentrate on the exercises and the muscles they are working. I like the way some folks describe these as "gym style" workouts because that rings true for me.
They are a great balance between the intensity of P90X while still being under an hour (most P90X workouts are 60 minutes w/ the exceptions being Cardio X (45 minutes) and Yoga X (90 minutes).
To speak specifically of Sweat 5-6:
This program follows the same format as the Sweat 1-2 and 3-4 workouts. They start with a warm up, then go to Power Yoga and then move into a series of athletic cardio moves. After those you get into a series of kickboxing type movements before the final cooldown.
One thing I particularly love about Sweat 5-6 compared to the earlier Power 90 programs is that Tony gives you a much more expanded warm up section. In the Original Power 90 workouts I always found that the first round of each exercise served as a warm up (which I did very much modified) and then the subsequent rounds is where I'd amp up the intensity. With the Masters Series I find I'm so well warmed up that I can start the actual workout part of the program at full (or close to full) intensity.
As I mentioned above, I find the Masters Workouts in general to be my favorite of Tony Horton's workouts and I really love all his programs. There is something about the whole vibe of the workouts, from Tony's demeanor, the "students" he chose for the workouts, the set and the music. Plus the fact that they are such a reasonable length makes them very easy to fit in most folks schedule. Also, the intensity is enough to give me a great workout without making me feel completely depleted.
I am a HUGE Tony Horton fan and I think he's at his best in the Master's Series. I find him to be relaxed, funny, and yet very motivating!