I'll be visiting DR for the first time from 23-31 December and staying with my 18-year old son at the Tangerine. Since this is an all-inclusive, no doubt there will be lots to do at the resort, however, I'm interested in getting out and visiting the local area. Any suggestions regarding siteseeing, nightlife etc would be appreciated.
Look at Debbie's Dominican Travel at
http://www.debbiesdominicantravel.com/viva.html
My review is the second one down, labelled John - Burlington, Ontario Canada. Do a search on "Mooseman" here on DR1 for other threads as well that say more about the local area.
The resort is fairly quiet, or it was when we were there in November. Great for us older folks, but an 18-year old will be looking for different action. The kite-board lessons might interest him and there are two places nearby that offer to teach. The closest one is just west(ish) of the resort on the beach and has a sign posted.
The resort has boogie boards and kayaks free of charge; just have to leave your hotel card with the staff that hand out the equipment. There is also a small catamaran that has a small fee charged and you get someone to help sail it.
Walk up the beach to get to downtown Cabarete. Turn right on the beach (east-ish) and walk about 10 minutes until you see the bars that open on to the beach and just walk through to the street. Jose McShays is a decent bar and has a pass-through. The street was all torn up when we were there and traffic was horrendous. Watch crossing or you will be run over repeatedly.
If your son happens to like young women, there will likely be some there as well.

Look at some of the posts on DR1 about the way things are with respect to tourists and residents, either gender and act accordingly.
Travel back to Sosua for sure - don't miss that town. Either take a taxi, about $10US, or flag down a public car on the street outside the resort and pay the driver 25 pesos each when you get to Sosua. Look up Rocky's Blues Bar on Calle Dr. Rosen #22El Batey - Sosua
Rocky's Rock & Blues Bar and Hotel, Sosua - Dominican Republic for a great time, cold beer, pretty women and good food. Tell him Mooseman said hello.
Have a great time in the DR!