Nantucket simple seafood
Recommendations for wonderful, simple seafood in Nantucket--in-the-rough is great, lobster shack would be nice--but not essential--just honest, un-gussied up fare.
On Nantucket the best spot for straight-forward seafood is Sayle's Seafood, 99 Washington St. Extension - on the water. An easy walk from town. It's a seafood store that does a huge carry-out business. Lobster dinner, clams, chowder, etc. Eat your meal on their porch or walk down to the water. It looks like a hole in the wall but it delivers the goods. Best bang for your buck, too. Google it, I think they have a menu on-line..
There is a restaurant on Washington St to have a steamed lobster, clambake, or fried clams or fish. The Nantucket Lobster Trap. Nothing special, but reasonable quality lobster shack fare (at Nantucket restaurant prices). They have a casual patio to eat on. Not cheap, but you didn't say price was the issue.