I have it and am on day 9 of the 30 day challenge. It is a great fitness program, though the resistance band provided is way too light (thin). I picked up a 3 pack of resistance bands from Target for $8.99 with a light medium and heavy band, and am currently using the blue heavy band on the medium workout level.
The software provides a much better workout than Wii Fit. You will work up a sweat, and the exercises follow a program, working out varied muscle groups each day, with a consistent focus on cardio. It works you out and it works very well. It gives you an estimated calorie count of burned calories, and gives you extra points for healthy eating, water consumption, outside exercise, and good sleeping patterns.
I have lost more weight in the short time I've owned this than I ever did with Wii Fit. But I might add some Wii Fit into my routine as well, as the sit ups and pushup exercises in Wii Fit are not present in Active. Though I would use Active as the main program, and use only the strength and yoga from Wii Fit as the cardio in Active is much more effective than the cardio (lol) in Wii Fit.
My only complaint, though minor, is that the controls are slightly buggy in two of the twenty five exercises (Lunges, Bicep Curls with Shoulder Presses). The Wiimote and nunchuck are recognized by exact turns in these two exercises, and I believe the nunchuck doesn't always show the move.
Overall I'd give Active a 9 out of 10 as an exercise too, and Wii Fit a 7 out of 10.