Patbro, it would be good if you could tell us what you were looking for - it is easier to respond to specifics.
About Cabarete - The beach has a family atmosphere with lots of windsurfing and kitesurfing, swimming and people enjoying the water. The restaurants on the beach contribute to a colorful and always changing scenery. In the evening, the beach turns into one big restaurant with all the restaurants setting out additional tables on the sand under the palms. The beach hots up late at night and you'll find parties going on. I don't know the places that are 'in' at the moment. Just walk down the beach at night and you'll find them.
During the day, walk the main road and you'll find many activities and excursions into the countryside - horseriding tours, 4 wheelers, boat rides on the little river, longer excursions into the mountains for river rafting, bicycles, and a host of other activities.
I have not found any great snorkel spots.
About Sosua - The beach has a great laid-back atmosphere and it is quite a beautiful setting. Lots of tourist type shopping, small restaurants and so on on and around the beach and an active nightlife. Tours and activities of many descriptions are available - just simply take a walk around the place and you'll find the tour operators. The 'people profile' in Sosua is different and the atmosphere is quite different than in Cabarete.
About Puerto Plata - The beach is rocky and only very few people go to POP beach. The setting is not attractive but there are a few nice restaurants on the foreshore. POP is not a tourist town so much although just outside of POP, going to Sosua, is a one of those 'mini' racing tracks - I have not done it but it looks fun. Also, take the cable car up the mountain on a clear day. It is an excellent experience. The usual tours are available. POP has probably more All Inclusive hotels around than tourist type hotels, so, the atmosphere is not touristy and laid back as in Sosua and Cabarete. Also, just outside of POP, there is an excursions company with these great big trucks painted with zebra stripes. The tourists sit in the open back, which is quite high and has a secure railing and seats. I'm not too sure where they go, but the people on these trucks always look quite relaxed as if they're having a great time.
Lastly, do a search on this board for each of these towns and you'll be surprised at the specific information you get.