Funny you should mention it, but I just started using the Power 90 video last week. I am starting out slow, because it seems higher impact than I am used to and I am recovering from a back injury. I just did the first few minutes of the cardio as a test and had no ill effects - to my back, at least. It did, however, humble me a bit. I'm 55 and haven't done much high impact work for many years, decades maybe. It was pretty funny to see me try to do jumping jacks - I don't have much spring anymore, it seems. But for that reason, I decided that I would do this video once a week. Use it or lose it.
I don't have much to offer you with regard to your question. I have always tried to use a variety of videos to stave off boredom. But it is difficult to find ones that are pure cardio that I like. One I do like is Fat Burning for Dummies with Gay Gasper. It is very plan jane - grapevines, etc - but she keeps you moving at exactly the right rate to keep your heart rate in the fat burning zone, and I try to do that one once a week as well.