Mystic is quiet in the winter, a bloody zoo in the summer with all the Touroids (seasonal pains in the ass) coming to downtown, the seaport and Aquarium/Village (shopping). What you see now, is nothing like it is in July.

Stonington/North Stonington/Ledyard (in descending order of things to do/population density) are worth a look, as is Westerly RI (abuts Stonington). Westerly has the beaches and a really nice walkable downtown (arts/restaurants/events in Wilcox Park) without the mass of Touroids in Mystic. They're still around but it isn't anywhere near as bad