Nethack is a fun game, no doubt about it. It’s not whiz-bang pretty like a lot of the games out there, but it’s easy to fire up a Nethack session and play for a while. Plus it’s got a surprising range of playing options for such a simple game.
I haven’t really immersed myself into it yet, but I enjoy having a terminal window open with vanilla Nethack going while I work on other stuff.
