I just returned from my first visit to Puerto Rico (Vieques, Rincon, and San Juan). For Vieques, I want to add my vote for El Quenepo being one of the best restaurants anywhere. I also want to add the following to the list of recommended places, all in Esperanza except the last, which is in Isabel: Trade Winds, Bili, Belly Buttons, and Al's. Also, the café at the airport has great fish tacos.
In Rincon, El Fogon de la Curva was out of almost everything by the time we got there (it was 3 Kings Day), but what was left was delicious.
Stopped in Camuy for lunch at Fogon del Abuela. After 45 minutes, we took our order to go because it was so slow....and not that good.
In San Juan for 3 nights we had tapas and wine one night at both El Convento and Marmalade without reservations. A great way to sample the menus. The other two nights we went to Ferrari Gourmet on Ave Isla Verde, an Argentinian restaurant that doesn't seem to have been mentioned on this website. Their pizza and their steak are wonderful and the prices are good. The hospitality is very special as well. I'd highly urge you to go.