If you're an outdoors person, you can't beat Maine! We're an excellent 4 season wonderland! You can hike, fish, swim, suntan, bike, hunt, leef peep, ski, snowmobile, boat, see professional baseball and hockey games, you name it! Come any time of the year, for a week, 2 weeks, it doesn't matter, you'll wish you stayed longer!
Slow down and take a breath. Most places north of portland maine are nice and slow. You won't see 4 car crashes on your way to work or wait an hour to cross the road. Out of the small city areas it is so peacefull just to sit back and enjoy true silence
If you're interested at all in farming, there is a really nice network of small, organic farmers in Maine, particularly in the Unity/Freedom/Liberty area, but also along the coast. Eliot Coleman's farm is in Brooksville (sort of a farm celebrity) and most of them are happy to have people take an interest in their work.
MOFGA (Maine Organic Farmers and Gardeners Association) website, MOFGA.org is a pretty good resource for locating farmers and seeing whatever workshops and things are going on.
really... you just want one reason? Baxter State Park, Allagash River, Penobscot River, Moosehead Lake, the list goes on and on... just make sure if you visit that you travel further north than Portland/Freeport, and if you really want to do yourself a favor, make sure you head north and west of Bangor into the North Maine Woods.