Recs.
Updated
NetHack is a single-player roguelike video game originally released in 1987 with ASCII graphics.
Specs
Pros
Pro Challenging
Nethack is a very difficult roguelike with permadeath, meaning that all your progress is destroyed when you die. Most Nethack players don't fully beat the game until months or years later (if at all). However, the game still tracks your progress and scores even if you don't win, so it's fun and challenging regardless.
Pro Community game server at alt.org
There is a Nethack server at https://alt.org/nethack/ that allows you to play without installing the game locally. It also keeps a high score board so users can compete against other scores, knowing that the local copy of the game is not tampered with to prevent cheating. alt.org also has a new UI for playing the game in a browser.
Cons
Con Feature creep
NetHack has an overwhelming amount of features mostly because the development team found them cool at the time, but with little thought of their greater impact. For example, a Nethack staple is Sokoban as a built-in minigame, which feels out of place in a dungeon crawler.
The extremely large amount of items and abilities break the game's balance and coherence.