I recommend
Mariscos la Delicia - the Chef is former Captain Cook chef. I know the owner nice guy and can even accompany you for a small talk after the diner, if he is there. Good food, prices are ok for being the DR (where eating out is not cheap). They are on Calle Libertad, behind basilica, just half a block away form Laboratorio Referencia.
D'Yira Restaurant - nationwide famous Mofongo, people come even from far away places to eat there. They are on Hermanos Trejo, about a block from Claro office (if coming form 3 cruses they will be on your left side, if from Santo Domingo direction, on the right side). You have to look for it because the entrance is a bit of "hidden".
Besides that, there are not that many places to eat out. There are two more restaurants on Boulevard but they are not even much frequented by the locals.
Later at night, you may want to grab a drink in Mamajuana Cafe, on Juan XXIII just before reaching Carretera Mella (1 block away form Super Higueyano). It is a bit more intimate than the second option, Go Drink, on Carreterea Mella in front of Esso Gas station, where especially on weekend night huge crowds gather. (Carr. Mella is the road that goes from 3 Cruces towards El Seybo and passes Iberia supermarket).
PM me when you plan to go, if you like we can grab a drink or a beer.