Woods, ponds, and proximity to beaches at an affordable price
This park is huge! The 418 mostly wooded sites are divided into 7 sections and even more loops. You can find walk-in sites, tent sites, RV sites or yurts. The only thing missing is hook-ups. Water is readily available and there's a dump station, but you won't find electric. I liked some of the sites on the top and backs of the loops in the Section 6 area.
The attraction for me is the central location on the Cape Cod Rail Trail. Additionally, a number of beaches on Cape Cod Bay are only a couple of miles away, so you can easily bike over and avoid the parking struggle. There are bike trails in the park as well, but hillier than those outside the park. You can fill many hours hiking, geocaching, fishing, boating, and swimming. If you don't have a bike or a boat, they'are available to rent in or near the park. If you are seeking the dunes and expansive coastal beaches, you will need to leave the park and contend with traffic, but there's plenty to keep you busy without ever leaving the park.
Of note, the rates are quite reasonable for MA residents, but significantly higher for out of state campers. Even so, it's a bargain for the prime location!