My favorite ascii dungeon game, Nethack has tons of features. You can play as various types of characters like tourists, wizards, and healers. You can worship many different gods. You can go to shops, and you can even train your pets to steal from them! The main downside of Nethack is its thoroughness. Nethack has tons of features, giving it a really poor learning curve. However, tons of spoilers and secrets are available from the home page or from other web pages. Also, a long addiction to Nethack caused a tremendous increase in my typing speed (Nethack uses tons of different key combinations for various commands). If you enjoy rogue-likes, Nethack is one of the best.