Definitive New England seafood dinner?
I know everyone will disagree, and I've only been there once, but I had a good dinner at the Union Oyster House. It *is* a tourist trap and I'm sure you can get beter, but it is quintessential New England what with being the oldest restaurant in the country. Maybe go for a few oysters and check it out if you don't want a whole meal. I also agree with taking a ride along Clam Alley, aka Rt. 133 altho now's not really prime time.
Try Legal seafoods. High quality, dependable, but can be boring. Summer Shack which sometimes gets trashed on these pages, but mixes the idea of a lobster pound with cutting edge seafood at cutting edge prices. I enjoy it but you have to know what to expect. the Barking Crab on the waterfront with wonderful view of the Boston skyline. Get a car and take a trip to Essex and Ipswich for fried seafood at the Clam box, Woodmans, Farnhams, or Essex Seafood. or head to Maine, just a little more that an hour from boston. Enjoy!
It might have surprised you that you had yet to get a response to such a common question. Perhaps because there might be a little more to "authentic" than meets the eye.
Is your goal more of a "fine dining" (eg, high-end restaurant) experience? Or more of an "authentic local" experience (eg, beachside fried clam shack or local fish fry)?
Is is more oriented to finfish or shellfish?
That last question has become more key lately. The legendary finfisheries of the northwest Atlantic (400 years ago, so teeming with fish that the ocean looked liked it was boiling with them) have collapsed. A lot more (but certainly not all) of the finfish served here comes from aquaculture and importation, so there is likely to be more overlap with some of the finfish you already eat at home.
On the other hand, one consequence of having fewer finfish is that stocks of their prey -- shellfish -- have boomed in many places.
Lose much, win some.
Even though it appears that the New England clambake was more a product of enterprising 19th century entrepreneurs than an inheritance from Native Americans, for my money there is nothing quite like a real clambake at the beach on a mid-July (with the first corn of the season but before the greenhead-fly season) afternoon or evening.