We've been camping at Wellfleet Hollow (formerly Paine's Campground) for close to thirty years.  We love its location in the funky, artsy town of Wellfleet where there are great food options and some of the best beaches on Cape Cod.  It's also walking distance to the secluded Duck Pond which is a gem.  The campsite itself it wonderful with a tree canopy that lets in plenty of light but won't let you be baked with hot sun.  The sites are well spaced so you don't feel too crowded and the terrain is a bit hilly so it's got a nice, rustic feel to it.  At night you can go out to the power lines for some of the best star gazing on the East Coast. It's a short bike ride to the Cape Cod Rail Trail which is wonderful.  The bathroom facilities are much improved too.  The only beef I have is that out of staters have to pay an exorbitant fee relative to people from Massachusetts.  That seems a bit unfriendly especially since we are within the boundaries of the National Seashore roughly speaking.