i wouldn't recommend sosua, but cabarete is cool. cayo levantado in samana is extra nice
punta rucia has untouched beaches but is a bit difficult to travel to. you either need your own car or take a tour there if your hotel offers one. try to visit santo domingo, the colonial zone is really cool, lot's of bars and a cool nightlife
Zona Colonial, Santo Domingo, Dominican Republic: A Historic Caribbean Destination. also about the only chance to hook up with girls who are not whores (still not easy as a tourist though, because there is a stigma attached to dating foreigners). if you only visit the touristy places all you will meet are girls who are either hookers or try to be your girlfriend in order to have you send her money on a monthly basis. you can also go to santiago, the second biggest city, which is closer to sosua and cabarete. they have a cool nightlife there too, but its almost strictly dominican, so as gringos you will stick out like a sore thumb. jarabacoa is great if you want to relex dominican style, chilling at a river with a bottle of rum or whiskey, a pack of crushed ice and two bottles of sprite. you can also go rafting there.
wherever you go, don't flaunt your money too much, because it will either attract hookers and thieves or rub people the wrong way. try to adapt and pay attention to how people dress and behave. other than at the beach, you should always wear long pants with a belt, a polo shirt and no sneakers. otherwise, people will not take you seriously.