I tried it, a long time ago, for about 2 or 3 weeks, and lost a few pounds temporarily. I didnt like it. Diets based on starvation (aka restricting calories arbitrarily) dont work for me. It induces depression (with subsequent regain of the weight) and loss of lean tissue so that I became fatter than had I not bothered in the first place.
But if you like the system and you arent paying for it, I suppose you could give it a try, but dont be afraid to experiment within the structure of their system to customize it for what works for you.
Ultimately I dont have alot of faith that you will lose weight permanently on weight watchers. I personally have known dozens of people who have used it. Zero percent of those people have kept the weight off.
Given that you are morbidly obese, you will need a total body transformation that will affect all the systems in your body to become normal. The only transformation you've experienced of that magnitude is puberty and this transformation will take just as long (4 or 5 years), so settle in for a looooong ride.
Its not about motivation, specific diets or specific workout routines. As with any other major change in life, its about learning (research), experimentation, failures, adaptation, being realistic, making sustainable changes, being in tune with what makes us feel good and healthy and gradually turning the dial up on that.
If you are concerned about how fast you are going to lose this weight, you have already failed. If you're concerned about generally staying on the track that leads to health then you are guaranteed to succeed with enough patience and time.
If you are anything like me when I was your age, then you will ignore everything I just typed. Hopefully you are not like me and wont waste the next 15 years slowly killing yourself.