NetHack

The Good
The gameplay. It all comes down to that in Nethack. A quick description of the idea of this type of game: you descend into a randomly-generated dungeon, with an ultimate quest in mind. There is no way to save your game - once you die, you have to start the game over with a new character.

Nethack is basically just a hack-and-slash game, but there is so much to it that it never ceases to amaze. There are literally thousands of items and creatures. The important part of this is that all the items and creatures interact in just about any way imaginable.

The standard example serves well to exemplify the spirit of the game: lets say you kill a cockatrice. They're not easy to kill, seeing as how they can turn you into stone with their touch. But you've killed it. Now what do you do with corpse? Well, if you have rubber gloves on (so you don't turn to stone), you could pick up the corpse and then wield it like a weapon, so that when you hit enemies with the corpse, they themselves turn into stone. But the best part is this: lets say you leave the cockatrice corpse. Monsters could then come and use the corpse themselves to try to turn you into stone!

This is not an isolated example. This is not "one small feature" that has been added to the game. The whole game is like this!

Perhaps another small example would help. There are quite a few shops in the dungeons of the game. You don't have much gold to buy items in the shops though. Can you find a way to steal stuff in the shop? But of course! You could send you pet in and hope it picks up something you want. Having trained it well enough (training your pet is a whole other story), you can then call it back to your side, where it returns an item pilfered from the store. But perhaps your pet is dead. So you find a pickaxe, hide it in a bag so the storekeeper can't see it as you come in (they check this kind of thing), pick up an item, make a hole in the floor with the pickaxe, and drop down to the next dungeon level, safe from the storekeepers vengeance. Just don't expect to go back to the store any time soon...

Did I mention this game is free? And open-source? And available for any platform? (DOS, Windows, Linux, Amiga, Macintosh....)

The Bad
As much fun as this game is, it isn't the best game ever. It is almost certainly the best hack-and-slash game ever, but hack-and-slash has its limitations. As much depth as the game has, you are still just going around a dungeon, killing things, and doing some quests.

So, after a while playing, it can become a bit monotonous. So you leave the game for a while, but soon you return, to discover something else fascinating about the game, and then you play for a while longer.

The Bottom Line
Just try it for yourself. The ASCII graphics and keyboard interface can be a bit overwhelming at first, but it really only takes half an hour to get used to the game.

Once there, this is the kind of game you will be playing, off and on, for decades. Literally. Most people haven't beaten the game until they've played it for years - I doubt anyone playing knows everything about the game. It is a unique experience, and a great addition to a gaming library.