Going to the Caribbean is certainly different than WDW, but also a wonderful vacation. We went to Grand Cayman in March (had gone to WDW at the holidays just before, so it was fresh in our minds). At one point early on, my DGS, age 6 said it was better than WDW and he wanted to move there. Of course that quickly blended in to wanting to combine the two experiences and have the best of both.
There aren't the thrill rides and overstimulation -- but most islands have some tourist activities as well as enjoying the natural ones. If you like sun, sand, swimming (beach and pool), experiencing new things, etc. you will have a lovely time. I guess you could end up bored if you spend the whole time comparing it to WDW, or if the kids just want to play computer games.
We were in a timeshare that we really enjoyed and we like animal experiences -- seeing the turtles, iguanas, and especially the sting rays, and snorkeling to see fish.
I'd say give it a try -- it's always good to have some different experiences (and maybe next time you go to WDW, there will be some new things there for you to enjoy as well as your favorites).