I agrere that Harris' Crab House is worth the stop.
I also recommend The Suicide Bridge Restaurant on the Eastern Shore not terribly far from Easton. Even though it is not a crab "shack," it is a local institution that serves fresh seafood and it has a pretty setting on the Choptank River at an old fishing marina. They close in the winter.
If you get so far as Rehoboth Beach in Delaware, there's Crabby Dick's. It's good but not great, and there's no view.
I think the G& M place is the one I have been too a couple of times. Hammonds Ferry off the ring road. On the few occcasions I have been in that part of the world, I have had crabcakes there, and there are various sizes/quality; but I have always had the lump blue fin crab cake in a sandwich with fries and coleslaw ( enormous meal and way to big). the crab cake is beautifuly seasoned, there is no filler, and its immensely satisfying and tasty.
I have generally had to get a take-out from the side of the shop as the restaurant insde has been packed on the three occasions I have been there.
Harris' Crab House is the best crab joint I've been to. It's on the Eastern Shore on Kent Island, with a magnificent view and sunset, and a miniboardwalk (open only during warm months) next to it. It's not a "crab shack" in terms of a run down joint with wooden tables, but it's a nice restaurant that offers outdoor dining on wooden tables, indoor dining high wooden tables with large glass windows for viewing, and rooftop dining. I recommend the latter during warmer months.
I've been to Cantler's many times, and although the crabs were great there last time, nothing else there impresses me. Also, the view is just a creek and only if you sit outside, and you hope there's no one trying to park their boat while you're dining. It'll be very noisy, with tons of smoke spewing all over your food.
Crabs aren't in season locally. What you'll get in winter in the Chesapeake Bay region are shipped up from the Gulf Coast.
Here's a list of local favorites from Blue Crab, a good source of all things crabby.
Cantler's in Annapolis can usually be counted on to have local crabs when the season opens again. All of these have water views, none is fancy.