The only FREE beach resorts (meaning they do not charge an entrance fee) that we have been to are Paradise Beach and Mr. Sanchos.
We used to go to Mr Sanchos all the time, until Paradise Beach opened up. Mr. Sanchos does offer an all-inclusive, but Paradise Beach does not.
However, the most popular all-inclusive for adults is Nachi Cocom. It is great for adults who just want to lay in the sun...it is $49 a person for one 3 course meal and all you can drink. They have a swim up bar. However, any activities are additional...snorkeling etc.
Paradise Beach has the most water toys for the $12 wristband...and the wristband is OPTIONAL...so you can buy it for the kids and you don't have to buy it for yourself. (I hate having to spend money for something I will not use) It is the best choice for adults (or families) that want a lot to do.