The Fisherman's Coop, est 1976, is open year-round, but there is a most unpretentious "lobster shack" called The Rising Tide serving up fresh lobster that's only open during the summer and early fall. Don't expect anything fancy, but who cares! You have a stunning view of the water, lobster boats and lobtserman in action.
Late Sunday afternoon I had a Maine lobster dinner and watched a seagull eat a live clam after it dropped it on the ground to crack it open. Lobsterman paddled in and out from their boats and a truck hauled away one of the boats.
Like I said, the restaurant itself is very small and basic, true to "lobster shack chic," but so very satisfying if you love fresh Maine lobster and watching a working waterfront! You can see more views here.