I like plenty of games that put less of an emphasis on it, but I feel dungeon design is absolutely essential in capturing the spirit of what it means to be an RPG. As I've grown older, I still enjoy story and aesthetics but dungeon design and mechanics play a larger role in how I estimate a title.

It's part of why I enjoy the Dragon Quest games so much. They have such a delightfully novel intertwining of traps, puzzles, and layout that make the games more meaty than their peers. Final Fantasy V and VI are perhaps the only two games in the series that I would say had really great dungeon design, especially the latter.