There is absolutely no need for 4wd in Samana proper. I have been there many times in my little "puddle jumpers". with no problem. If you are going to Las Terrenas, the roads there are terrible, so you may consider it. Also if you are driving to Playa Rincon, although I have done both in a car and survived the ordeal. Obviously, if you are going off road or exploring on back roads in the campo, you will want 4wd.