Not to put down other "diets" but WW is really a lifestyle change for me rather than a diet. Cambridge Diet works but is very extreme but I don't really think it teaches people much about eating real food and nutrition. WW teaches you portion control and encourages you to eat plenty of nice fruit and veg. It will allow you to achieve steady weight loss and learn good habits for life If you look through other people's profile stats you will see that people have been able to achieve 2lb + losses per week!
I hope you keep with it because at least for me losing weight and being control of what I eat has made me more confident and happier. Hope that in a few weeks you will still very happy with your decision.
Best of luck, trust me if you have managed to stick to Cambridge then WW will be a doddle!