Have You Played? is an endless stream of game recommendations. One a day, every day of the year, perhaps for all time.
Ancient Domains of Mystery (ADOM) might be my favourite traditional roguelike. To some extent, the ranking depends on my mood, but ADOM has a remarkably well-tuned sense of progression to go along with the usual cluster of quaffable quandaries and randomised dungeoneering. Its sprawling depths are as perilous and perplexing as the pits of Moria and Hack, but the overworld is a fixed entity, with settlements and themed dungeons placed across it. I've played it for as many hours as any other game in existence and still find new challenges to overcome whenever I visit.
For those who came to know the term roguelike in recent times, ADOM is a fine entry point into the genre that spawned the term. The overworld structure and storyline of encroaching chaos offer stronger incentives to push onward than the usual dungeoncrawling objective. Many foguelikes simply ask you to go deeper until the magical macguffin is in your grasp but ADOM presents you with a firmer sense of purpose and belonging in the world.
It's also far more accessible than it was when I first played it back in the mid-nineties. Recent releases have attractive tilesets built in so you won't have to worry about plugging them in yourself, or deciphering ASCII symbols to understand how many dragons are in the room with you. I still prefer the ASCII graphics but that's what years of playing does - familiarity can make stubborn fools of us all.