I am a firm believer in the whole idea where some things work for you but not for others.
Meal replacements is something that DEFINATELY does NOT work for me, I dont have a car so walk everywhere, I go to the gym, I do runs with my partner and I love exercise - I'm fat because I couldnt stop eating, I was always hungry (physcologically and also due to the exercise) so a meal replacement meal for me was always a bad idea. I did it and lost the weight but I put it straight back on because I found it wayyyy to restrictive. I'm doing calorie counting now and will know from next week if its working for me, but I already have a sneaky suspicion it is! I was just eating the wrong foods before (way too much fat basically - lots of chips, cake etc)
However...my Mum has already lost over 20kg using the Optifast diet, although she started on the 2 shakes and a meal one with a slower weight loss and also allowing her to eat anything she wanted (within reason fo course) for dinner. She is still doing really well and is about to hop onto the next phase which is replacing her breakfast shake/bar/soup with a real meal and believes she'll shed the last 20kg off (she has lost lots of weight). She looks and says she feels amazing and I think because shes sticking to the plans, her doctors orders and is now at a gym under a careful programme she'll be ok. You just have to be able to stick to it and have the right mindset (wish I did!!!).
People want a quick fix, but it doesnt happen - even with Optifast my Mum took 8 months to drop that weight, and she's still got a fair bit to go!