This is the best seafood in Madison. Bar none. The crab cakes have huge chunks of crab which is always expected, but not always reality when ordering such a dish. The bottom line is that you can get any fish dish on the menu and be extremely satisfied.
I even had a friend from Chicago call to ask for suggestions on taking out a client on a sales trip. She incorrectly assumed that Madison would not have much in terms of food (which is outright WRONG), but it's hard to blame her since it is a smaller town in Wisconsin. I digress - I pointed her to the Blue Marlin and she was extremely impressed.
It's also a smaller little place right on the corner of the capital square. An old roommate of mine LOVES oysters and this is the place to get the best in Madison as well. I'd recommend going here during restaurant week if you are on a budget since it is NOT cheap. So, make sure to budget appropriately for a solid dinner out one of these days and enjoy one of the many gems that Madison has to offer.