Yes been a few times as I have friends who live there. its probably one of the best places to learn kitesurfing/windsurfing if thats your thing.
If you are in the Puerto plata area then do the 27 waterfalls trip such great fun climbing up falls and jumping/sliding down others great day out when its hot. hotels organise trips but you can just turn up too. it is run by the local community and they are very proud of it.
+1 for santo domingo great place to spend a couple of days
+1 that there are some pretty nasty looking all inclusives but i’ve never stayed in one
Hotels may tell you that its dangerous on your own and you need to go on organised trips but its really pretty safe, so long as you are sensible and remember it is a very poor country.
We have helped out with some charitable work out there too such as http://sosuakids.com/ they always need help with equipment etc.