Zumba

I agree with marymooster. Any exercise is good!
On the other hand though, you are right also. I have been addicted to Zumba for 2 years now. Front of the class, memorized steps. . . etc. lol I do not feel it has helped with weight loss possibly weight management but definately not weight loss. I just go because it gets me moving and is a ton of fun. After class though I will do some light weights.

I'm not an expert by any means but I have tried many types of work-outs throughout the years and I'm recent trying to lose weight and build my fitness level. Zumba is a great exercise, I've been going sporadically for the past 9 months or so and I find it to be really fun! The intensity really depends on the instructor, if you follow their high intensity example if you are able, you should be burning many calories. I'm certain you're getting a really good workout but what I noticed is that I was having so much fun, I did not seem to notice how much I was working. Zumba is really good cardio so if you enjoy it, stick with it. On the in-between days, you should consider doing some brisk walking. It won't kill your knees or back (it should help improve them) and it is really beneficial. Both of these exercises will help you build your fitness level and strengthen your muscles should you want to do something more intense later.
In terms of core/strength training but also getting some calorie burn, I HIGHLY recommend Pilates. Building your core muscles will not only make your cardio easier, it can also help protect you from injury. Start with a beginner course as it can be challenging at first but in just a few weeks you will notice some muscle definition if you are truly utilizing the work-out.
Lastly, I recently had a light bulb turn this summer on when I did a 'fitness challenge' at the local YMCA for six weeks. I worked out 5 days a week with some good intensity. I was so sore! But at the end of the 6 weeks, I only lost 2 pounds. Why? Well, because I really didn't change my diet. I didn't track anything and it was almost as if I was justifying eating the same because I was working out so much. Tracking my food has been a tremendous help, kept me honest and helped me make better food choices in my 'journey' to get healthy and fit. I'm starting to see results. Anyway, I hope some of this information will be helpful to you. No matter what, just keep moving :-)

I am a zumba instructor and certified athletic trainer. I have taught various Zumba classes with different degrees of difficulty. I'm not sure if your main concern is your knees or sweating more? If it is your knees then I suggest a more low impact exercise such as water aerobics or elliptical for cardio. If the workout isnt burning enough calories for you try a different class. I also teach BodyPump which is a full body barbell class. This class is low impact with no jumping, but the intensity becasue of the weights make you drip with sweat. My best suggetion for you is to talk to your instructor or a trainer and find out the best course of action to maximize your weight loss.