NetHack

NetHack is a critically acclaimed Rougelike that fully deserves that title. In NetHack you explore a procedurally generated dungeon attempting to survive, collect loot, and find secrets. The game is turn-based in that every time you do something everything else gets to take an action as well, in the style of the original Rouge or the Pokemon Mystery Dungeon games. The game features perma-death, so every time you die the dungeon is remade and you start all over again. You also get to customize your character by choosing between a variety of races, classes, and obviously m/f. The game has pretty good depth, but it's all very well documented on the website. Documentation can be found here. It should also be noted that the game can be rather difficult and you will probably die quite a bit.

My opinion: I love Rougelikes and Rougelites, and NetHack is a very good Rougelike. It's got essentially infinite replayability and more depth than you're likely to find in any other game in this genre out today. The only issue I think more current fans of Rouge-inspired games would have is ironically enough the turn based aspect of it, despite that being how the genre originally started. However nowadays the way most people know games like this are as Procedural Death Labyrinths with a focus on precise movement and kiting over in depth RPG-style combat. So, while this game might be completely perfect for long time fans of the genre I'm not sure how it would go over with people who prefer the direction more modern games like this have taken.

NetHack is by Stiching Matematisch Centrum and M. Stephenson. You can find it here.