Susan,
In my opinion (just to chime in here, I know you've already got several replies), C/S and Circuit Max have but one thing in common-the fact that they are circuit workouts. Oh, and they're both fun, too! But CM is way, way up there on the intensity scale compared to C/S. I wouldn't put them in the same category intensity-wise. I just did CM for the second time last night and IS IT FUN! Gosh, Cathe has you completely worn out at the end, mentally and physically. There is so much going on with the different styles of cardio that it is completely, thoroughly entertaining. The strength portions are very short and add to the interest of the whole workout. The one thing I will say is, because the cardio segments are so short, there is not alot of choreography build-up. You sort of have to catch on to her moves as she is doing them, but it isn't too hard because Cathe's cueing is so fab. I'm a newly-brave, former-choreography-challenged sort of person, just so you know where I'm coming from (my only two other Cathe cardio's right now are Cardio Kicks and Wedding tape but pretty soon I'll have many more to choose from).
hope this helps.
Kathy