It's not high end, nor gourmet, but for a burger, drink and a view it's pretty acceptable. Just stay away from the regular entrees. Paradise Bar and Grille, on the Stamford Waterfront. For a better (and more expensive) experience, L'Escale in Greenwich is excellent.
Schoolhouse at Cannondale is top drawer in every way, although the waterfront is the Norwalk River, not the LI Sound. But the place is wonderful, and there are tables right on the river.
there is Splash in Westport - very good pan asian food. fabulous calamari salad.
not sure if rowaytan seafood is on the water or close to it - delicious food
there's also a high end restaurant in norwalk that overlooks the water that everyone loves but i had a horrible meal there