Brennan's is not masquerading as anything but what it is. They do fish, and they do it well!
My husband and I split the New England clam chowder and the perch and walleye combo. The clam chowder was okay. Honestly, it tasted very similar to the canned stuff you can get at the grocery. I wouldn't order it again. The fried clam appetizer was tasty, as well as the perch and walleye. Fries were greasy and delicious. The highlight was definitely the walleye.
All in all, if you're looking for laid-back atmosphere, fish and beer, you've found the place.