I think Powerstrike tapes are the most effective, authentic kickboxing tapes around, and I love the rapport between Illaria and Patricia. That said, I don't think the Millenium Series is the best of the bunch. They produced a dozen or so videos previous to these (that are probably no longer available anywhere) and even though the camera work and the sound are both rather amaturish--horrible in the earliest ones--the excellent workouts make up for it. I really feel well worked when I've done a Powerstrike workout, and there's nothing I find "too fast to be safe" as there is on many Tae Bo workouts. They also stick with kickboxing moves only and don't add in any other choreography, so are space efficient. And Illaria's form is impeccable.
Of the Millenium Series, I and II are better than III, IMO. I like III, but it gets going a lot slower, and it feels like a beginning workout (or as close as PS gets to one) for the first 18 minutes or so). The camera work is also back to being odd in this one. It's odd that they chose this one to try out DVD.
