My wife and I visited The Marshside last year in the off season and took our family back there this year on the first day of July. Both visits were very satisfying in terms of ambience and food.
The restaurant accommodates families well and also is able to sit adults in the outer perimeter so as to give them a little more privacy. The view of the marshes is, as the name implies, spectacular and restful. There is also a full bar. Our service was excellent and the food was very good. The onion rings are thin, lightly breaded, and about the best I've ever had. All of the other items we ordered were very good. While it is Cape Cod, the prices are both fair and reasonable. Some reviewers complained of the wait, and since the restaurant does not take reservations, that could be a problem. We got there at 11:30 when the restaurant opened, so as to avoid any waiting. If I would recommend anything, it would be for the restaurant to consider some kind of online reservation service. Be sure to pick up some baked goods upon leaving. We got the chocolate chip cookies, and they are as good, if not better, than what grandma used to make--they are also huge.