I've been to Dexter's fish fry on multiple occasions. Their basic beer battered cod is among the best you'll find. The perch is multiple small portions of fish. It's good but not great. I can't speak for the walleye or shrimp because I always get the beer battered cod- it's that good!
The only drawback is the wait on Fridays expect an hour plus. They have a great beer selection to entertain your taste buds while you wait.