Hi Thea --
Jazzercise is an great cardio workout and it's up to you to make it either high-impact or low-impact. I went to Jazzercise for 11 years ('80's through the mid-90's) and I credit Jazzercise with taking me from thin but sedentary to very heart-fit. My first class I thought I'd never make it through the warm up. That tells you how sedentary I was.
At the time that I went to Jazzercise, it was only cardio, no weights. I went to a few classes a couple of years ago that had a weight section but they were too light for me. I had joined my friend for a few sessions. The only reason I didn't go back to Jazzercise as one of my "off" sessions was parking, not the work out.
In my experience, the instructor and her taste in music is one of the biggest factors as to whether you've enjoy the workout. I understand that the routines are choreographed to various styles and it's up to the instructor to select the music style she likes.
Jazzercise has a socialization aspect that is missing from doing videos at home and this can provide an "accountability" that a lot of people like.
Juli