Heh. I brought NetHack up recently in the Entertainment/Gaming Consoles thread that never dies...
The beauty of NetHack is that there are _so many_ ways to die, yet so many logical ways to save yourself that generally escape you until after you're staring at your tombstone.
<a href="http://www.hut.fi/~eye/roguelike/">This page</a> provides a nice insight as to the history of "Roguelike" ASCII dungeon-crawl games, and how the code forked from the original:
<pre>
Rogue--------------
/ \ \ \
Hack Moria Omega \
/ \ \
NetHack Angband---- ADOM
/ \ \ \
Slash'Em Falcon's Zangband Dozens of other
Eye *angband spinoffs
</pre>
Zangband is my favorite, and one to which I contributed minor code for a (now-obsolete) release. I've burned major hours on Rogue, NetHack, Moria and Angband, however, and would recommend all.