The Seamen's Inne Restaurant and Pub, next to the Mystic Seaport as you're driving into this historic port town, offers a good selection of pub grub and more formal options. They have lobster rolls, amongst other seafood fare. The pub has a nice outdoor patio and garden that offers scenic views of the water and the Seaport's tall ships. Although I haven't eaten there, you might also try The Cove Clam Shack & Fresh Fish Market (20 Old Stonington Rd.), which garners rave reviews for its fresh seafood and lobster rolls.