Not an easy one to answer. I've known people who've lost plenty of weight on the Atkins diet. But, what it did to their cholesterol, etc., is another matter. Few kept the weight off, but then again, few people on any kind of diets endure.
IMO (and this opinion is from a guy with a constant weight problem), the reason you gain weight is because you're eating more than you should. The way to lose weight and keep it off is to eat less of everything--not to find a diet that lets you continue to overeat only certain foods, as per Atkins.