NetHack is loads of fun. I have been playing since around 2008 now, have ascended 11 times, know a ton about the intricacies of the mechanics, and still find it a lot of fun.
I would say there's a small amount of nostalgia in the game for me, but nothing like the NES & SNES games I played in childhood, more than a decade before I even tried NetHack for the first time. NetHack is pure ASCII (at least that's how I play it) with no sound or music whatsoever. Most of my nostalgia for games comes from sound, music, atmosphere, and story. NetHack has a little bit of story but zero character development. Your character is just a vessel for inputting commands into the game, not a character in any dramatic sense of the word.
What makes the game so compelling, for me, is the grand challenge of figuring out what to do with the dungeon (and its contents) the game throws at me on each run. Sometimes the dungeon can be brutally unforgiving and extremely stingy with resources. Other times, it can feel ridiculously generous (only for you to make a dumb mistake and lose it all). Either way, the game is always throwing something new at you, even when you've been playing it for decades!