Deer Isle is about as authentic as you can get.  Year round, the population is mostly families of fishermen of one sort or other, althhough there's a robust artistic community, as well.  In the summer, the "summer people" arrive.  My parents were summer people for their lives, then retired 30 years ago and now live on Deer Isle; my sister lives there as well.  When I was in high school, I lived there and had my summer jobs there.  Now I come to visit family, but also for the occasional vacation.  So I know Deer Isle both as a summer person and as someone "from away".  You can only be a native of Deer Isle if you were born there :-)

Deer Isle is about 45 minutes away by car from Bar Harbor and Acadia, and has a bridge from the mainland. 

As a tourist, Deer Isle is a wonderful place to go.  You won't find many accomodations, but during big family gatherings, I have stayed at both Pilgrim's Inn and Goose Cove Lodge.  Pilgrim's Inn is lovely, with nice rooms and a dining room, and a great bar right in Deer Isle villiage.  Goose Cove Lodge is set on conservation land and has wonderful views with very sparse cabins -- just the bare necessities.

There's plenty to do in the summer.  Bicyclists and Kayakers love the place.  Sailing is breathtakingly beautiful.  Visit galleries and Haystack (the artist communities) on foggy days.  Isle au Haut is accessible via a ferry from Stonington and is a lovely place to walk around and visit for a day trip.  Camden is a nice town to visit -- but I think it's main attribute is that it provides a backdrop for Deer Isle's incredible sunsets.

I find all the other seasons beautiful: winters are stark, and Spring, which comes around the end of May or June, is wonderful.  Weather is unpredicatble except for in July when it's generally sunny and not too hot.  August can be beautiful, but there have been many times when there are several weeks of fog.

Tom H