First off, a "real" all-inclusive includes meals, activities, drinks (including alochol), and of course loding. However, some do not include alcoholic beverages and they usually do not include sports such as scuba or escorted touring. The most important advice is to read what is included carefully, as each resort is different.
There are all-inclusive for families that include kid activities through out the day - some even have night time activities; there are some just for couples and others for everyone. Once again, read carefully, if you want a romantic or quiet vacation, do not go to an all-inclusive that says it is for “everyone”.
If you are looking for relaxation, beach and to be catered to without much exploring and adventure, an all inclusive in the Caribbean/Mexico is the perfect vacation for you.
The Dominican Republic, Jamaica and Mexico are probably the least expensive and most popular destinations in the Caribbean for mid - high level All Inclusive resorts. The Dominican Republic (Punta Cana especially) is perfect for all inclusive because it is not the best place to explore on your own. The resorts are safe, beaches are beautiful and you get the bang for your buck!
If you are coming from the West Coast, you may want to consider the All-Inclusives located on the West Coast of Mexico. There is a lot to see in Mexico, but because it is so inexpensive, it does not hurt to pay for the all inclusive to have the luxury of everything you need at your finger tips and go out every once in a while if you feel the urge.