If you want the super fun experience of shucking and BBQing 'em yourselves, Hog Island Oyster Company is where you wanna go. It's especially a great place for groups. But if you're only a party of less than 4 and you're lazy, in a hurry, or exhausted after 6 hours of kayaking, the Marshall Store is PERFECT.
FOOD: We got half a dozen BBQ oysters, half a dozen raw oysters, half a dozen Rockefeller (cheese and spinach), and a large clam chowder. The BBQ'd oysters were DELICIOUS, definitely my favorite. The Rockefeller oysters had more spinach than flavor.
The BBQ sauce that came on the oysters was thin, smoky, and slightly tangy. Be warned: the BBQ sauce in the bottle on the table is NOT THE SAME BBQ sauce. The BBQ sauce on the table is REALLY, REALLY spicy.
The clam chowder is really good, I'd say the second best in the area - IMO, Swan Oyster Depot's clam chowder claims first prize. The Marshall Store's clam chowder is authentic (I think my New England grandmother would approve) - it definitely tastes like the sea! From their selection of beers, I picked the Lost Coast's Tangerine wheat beer and I LOVED it. Very fruity and refreshing, easy to drink.
ATMOSPHERE: A seafood shack that looks like it used to be a house - it's definitely casual. You order at the counter and if you got clam chowder, you even ladle it yourself. You can buy wine or beer from the fridge, but you can't drink it inside. There's some charming, makeshift tables outside RIGHT BY THE SPARKLING WATER - perfect if the weather's nice. We thought the prices were super reasonable ($10 for half a dozen oysters). The service was fast and friendly (they'll deliver your food for you if you're sitting outside). The only downside was: no real bathrooms, I hate port-a-potties.