The workout is not at all strenuous, but is excellent for joints, flexibility, and muscle tone. I like to use it in combination with Rodney Yee's "Yoga Conditoning for Athletes," on days when I don't train. I also recommend this tape to sedentary people, because the gentle, no-impact moves are excellent for circulation and stress relief --- plus they feel great!
If you're interested in learning classical Tai Chi as a martial art, the best thing to do is find a good (live) instructor. However, if you're looking for gentle exercises to improve flexibility, circulation, and muscle condition, this is one of the best workouts you can get.