Nethack is a descendant of the early computer role-playing game
Rogue, in a category known as "roguelikes". As a roguelike, it is a turn-based single player game with primitive graphics. By default, the graphics are no more than ASCII characters (for example '
@' is you, the player). This puts it squarely in opposition to modern mainstream RPGs, which focus primarily on fancy 3D graphics, accessibility to wide audiences, often multiplayer support, and of course
making money. Nethack and most roguelikes are free, open source games.
Yet this style of game remains actively developed and played. Why would anyone play such a primitive antiquated game? It's challenging, but actually it's not the simple graphics that make it so. There is a depth to roguelikes, and Nethack, that isn't captured by most modern RPGs. Their beautiful graphics and interfaces present only part of the complete role-playing experience. For example, Nethack requires you to eat, but you might eat the wrong thing and get food poisoning. You might survive by chance or you might find a way to cure yourself. Similar to real life, it's incredibly easy to do something stupid in Nethack and die as a result. And by the way, you can't save - so if you die, you're gone forever unless maybe your ghost returns to haunt later players.
However, the game isn't rigged against you, there are ways to avoid stupidity and survive. But it's difficult - and therein lies the challenge. You get as much time as you need to analyze the situation and make each move. The game rewards cleverness and ingenuity. One of the unusual aspects of Nethack that is avoided by the typical RPG is the unknown nature of magical items you encounter. Whether it's a scroll, amulet, potion, ring, armor or weapon, you can't blindly trust that what you find helps you. Nor should you become particularly attached to your found items, which can and will be corroded, rusted, burnt, blown up, stolen, cursed, and so on, unless you find a way to protect them. Adaptability is a good thing.
Nethack is less straightforward than the modern RPG. Yes, they feature interesting quests with numerous NPCs. Yes, they introduce dramatics and build emotional connections. Yes, they take many hours to complete - but it's practically guaranteed that you will win if you spend that time and follow the prescribed path. Then you buy an expansion pack or download a mod to extend the replay value of the game. Most Nethack levels are random, you will experience a different dungeon every time you play. And choosing a different race, class, and alignment will drastically alter your choices. Some are extremely difficult to play, while others lend themselves naturally to the hack-and-slash style of play.
As you play Nethack, you will discover more and more about the game that you never realized before. Isn't that interesting from such a primitive game? I have read spoilers, so I know many aspects of the game that increase my appreciation of it. Play it once and you'll never see that depth. The label "hack-and-slash" is actually misleading - if all you do is attack things, you won't last very long. More important is knowing when and how to run away, and sensing danger that is beyond your character's abilities (a
mind flayer, for example...)
If the ASCII graphics feel too primitive, there are 2D tile sets available. Some variants of the game even have pseudo 3D tiles. I always enjoyed Slash'EM, which is a variant with many added items, classes and races. While the game was traditionally played only with keyboard commands, new ports have a mouse-friendly UI. Still, it's a lot to take in and certainly not for everyone. This is a game to lose yourself in and let hours go by, not looking at someone else's vision of the monsters and environment, but using your own imagination. It's a very "geeky" game, full of references to fantasy literature, appreciable to the D&D crowd.
Rogue is a classic, and roguelikes are an underrated but flourishing genre these days. Among them, Nethack is one of the best roguelikes I have played. Others to check out are Slash'EM and
Angband, each catering to different types of players.