I joined Curves late last year and really enjoy it. I get bored very quickly and what I like about this program is that every 30 sec you change equipment. I do about 2-3 circuits and it feels as though the 30mins is up in no time at all. I also feel stronger. There are 5 people at work now all joined up and we all enjoy it. Each centre is run differently so I recommend trying out other centres with a travel pass if you can. The one near my work plays games whilst you work out like trivia and the one closer to my home plays music and they have a staff member in the centre of the circuit encouraging you. I much prefer that as the music keeps me pumped.
My sister (in Brisbane - I'm in Sydney) has also joined up with a girl from her work. We have a family doctor in Brisbane who does a lot of work with morbidly obese people and he says that weight resistence work outs are very good for weight loss (provided you are putting out more than you are putting in).
I haven't had my first weigh in yet but will do in a couple of weeks. It's probably more expensive than most gyms but with Curves I don't have to think about what I'm going to do. I just join in the circuit and go for 30 mins. There is a little voice over tape that tells you when to change stations each 30 sec. They also do a heart beat check regularly and have a table so you can make sure you are working out at the correct pace.
Let me know your thoughts after you've been. I hope you find a program that suits you - exercise is so hard if you don't enjoy it!