Rustic, rugged, and simple, like my parents liked it, most of the time. With the kids, seaside meant Cape Cod but, for their together-getaways, it was always Monhegan (or Europe). For long-weekend getaways, it was Mohonk. Of course, there was always the Farm too, as lovely as can be in the Massachusetts Berkshires and a short drive to Tanglewood and close to plenty of fun ski areas.
I love the Maine woods for hunting and fishing, and the crazy state of Maine in general (to visit) but my problem is that the water is too cold for comfortable swimming, unlike the Cape where it is just invigorating.
A family friend just sent me this snap of my Dad (L) and my Mom (R) with a friend on the friend's lawn on Monhegan Island, Maine. My parents had 5 kids at that point, so it was good for them to get adult-oriented breaks.
It was Monhegan traders who taught English to Samoset, the sagamore who in 1621 startled the Pilgrims by boldly walking into their new village at Plymouth and saying: "Welcome, Englishmen."
The list at that Wiki link of the artists etc. who have had summer homes on Monhegan is impressive.
Photo below is the harbor, with the Island Inn. 17 miles of hiking trails.