"Is this fun" and "is it something a person in their 20s would want to play" are entirely different questions.

There are people who absolutely thrive doing the things NetHack rewards you for in the long term: perseverance, patience, planning, resourcefulness, risk management, strategizing, analyzing and learning systems... I feel like it has a timeless and ageless appeal to a particular kind of player and has never been quite palatable to mainstream audiences. If you like NetHack today you probably do it for the same reasons you would 30 years ago.