Simply the Finest Game Ever WrittenI've played this game for something like at least six years now, possibly longer, and it's still something I play to this day. I've completed it over a dozen times, with the majority of classes (IIRC, only Ranger and Monk are eluding me so far). It takes roughly 3,000,000 points to get into the top ten highscores on the version running on my psion. I even have a couple of mentions on the tables of http://alt.org/nethack . And even now, it still fascinates me.
Partly it's the replayability. Every game is different in some way, and every game (or at least every game where you don't die in a couple of hundred turns) something you've never quite come across before happens. Partly it's the fact that it's still an evolving game. I say this slightly tongue in cheek, because three and a half years since the latest version is getting a little... tardy. Still, there's always Slash'EM.
Mostly though, it's just... fun. Hard to describe why :)
Wolfechu 31-35, M 1 Sep 8, 2007