Returned to Mac's on the Wellfleet Pier twice during our vacation. Be aware that this is a seafood shack. The seating is outside under umbrellas on picnic tables. The bathroom is across the parking lot near the Harbormaster's building.
Over the 2 visits we sampled the fried oysters (best I've had since my childhood on Long Island -sweet, juicy, perfectly cooked), full fried clams (large, and evenly battered), kale soup (generous amounts of sausage and kale though not the depth of flavor you'd get at other restaurants) and steamers (large, sweet - add butter yum!).
Fresh, quality seafood is not cheap and you will pay upwards of $40-$50 for 2.