I thought about this when i played Soulhackers 2. That dungeon design was boring and very horrible in execution. I hate teleporters in any game and for some reason the radomized Mementos in Persona 5 doesn’t annoy me as much as the soulhackers 2 equivalent. I’m know what i don’t like, but i’m not completly sure what dugeon design is good in my opinion. I doesn’t like dugeons or route that always look the same, a maze with each position that look the same, so i guess i like dugeons more that vary about the design a lot. Funny the first that came to my mind is Kingdom hearts, i think those maps are change ennough to came to my mind. Or i remember that World of Final Fantasy was good in my opinion as well. But i’m sure you have better examples
I think what’s good depends on what the player is looking for. Some people prefer plenty of puzzles to work with, others want their endurance tested, others like the aesthetic, or other factors. As a general example, you’ll often hear Final Fantasy VIII’s final dungeon cited as a favorite due to its routing, puzzle and boss design, and its overall atmosphere.
My personal favorite dungeons are those that make me forget I’m in a dungeon or the ones that really excel in certain areas. Persona 5’s casino is a great example of the former because it’s so thematic and it does an excellent job of breaking up the gameplay in a different way. It’s a very different experience for the series. For the latter, I love Trails from Zero’s final dungeon. Right away it starts with a big dose of fan service for those that played the previous games, it has kickass music for the main theme itself and its boss themes, and it does a good job of feeling like a descent into hell. It also plays a major role in the overall arc of the series, too. Beyond that, the nuts of bolts of the dungeon design aren’t anything extraordinary: a few branching paths, some levers to adjust paths, the usual. But it’s still super fun because it nails those first qualities.
Etrian Odyssey probably has the best dungeons if you’re into map drawing.
For more traditional JRPGs, I prefer puzzle dungeons. Golden Sun and Lufia come to mind - although I cannot think of anything recent. At least not good ones, modern puzzles are often tedious but easy.
For action RPGs, Dark Souls and Bloodborne are probably the best I’ve played.
The common denominators between these are: You’re rewarded for being thorough, they aren’t fully linear (but it’s mostly clear where you should be going) and you cannot run through them mindlessly. So I guess that’s what I think makes a great dungeon in RPGs.