It has spawned numerous websites, user groups, mailing lists and Usenet topics. It has been around for decades and yet it still has uncounted adherents. It is, perhaps, the best game you can install on your Macintosh. It is Nethack.
Nethack is a first player adventure game. You enter its dungeons searching for treasure and fighting off monsters like trolls, and dragons, and newts as you become embroiled in various quests depending on the type of character you play: elf, ranger, knight and so forth. Sure, it has crappy ASCII graphics and a learning curve that is, to say the least, steep--at least for the purists who play it in Terminal. (There is also a Carbon version available, but it somehow fails to match up to the good old ASCII style with its intricate character-based commands.) Playing Nethack can take minutes, days, or when you start getting good at it, months.
Many Nethack players have been doing so for decades because it's that good a game with that level of intricacy, humor and detail. So if you've had it with Bejeweled and Chess and those Big Bang Board Games, consider investing a few hours or days into learning Nethack with its long term entertainment payoff.