What's wrong with 8-bit dungeon design? Anyways, Schala had some neat insights on FF4 dungeons in the anniversary thread, you just have to dig through some weirdo nonsense about Batman or something first haha.
But yeah, the dungeon design in terms of the aesthetics/tilesets in FF4 and some of the maps are relatively decent. Some of them can be frustrating to go through for some due to the handicaps implemented in there (ex: Sealed Cave's Trap Doors which are basically a way for you to level up so you can be prepared for the difficulty spike ahead; Land of Summons and the Sylvan Cave essentially forcing you to meet the required level of 38 or so just so that Rosa has Float and you'll be adequately prepped for the dungeon, Magnet Cave preventing you from using metallic weapons and feeling relieved when you finally could, etc.), but a lot of the time, the branching paths included in some of the dungeons are kind of creative (and sometimes are a little cute because some of them don't lead anywhere special).
I dunno. I thought they were designed rather well most of the time.