As the title says - you will get a good workout from this, but it isn't so hard that you would give up completely. I would say do be careful if you are new to exercise, it is a tough workout, and I wouldn't recommend it for anyone with joint problems due to the nature of the moves and because there is little modification available for more tentative exercisers. Have a look at the reviews on the American .com site for some more infos, I'd echo what's already on there. There are also negatives for the amount of talking this lady does - and boy does she talk - she never shuts up! However, rather than annoying I find it motivating, especially when I'm starting to flag and she constantly reminds you of form, which I find helpful. We'll see if she gets more annoying as time goes on, I haven't had it long yet.
I am fairly fit, I speedwalk everywhere and take weekly self defence classes. This DVD isn't massively about kickboxing skills so don't buy it thinking that you will learn how to defend yourself, but it will improve cardio fitness and stamina immensely, and help you with your co-ordination and core strength, whether or not you do some other kind of martial art or self defense. I wouldn't say it's a good alternative to actual kickboxing classes (which I also do) but can be complementary for these reasons.
The whole length of the DVD is 90 mins, which for the price and content is quite good value for money.