If you're not familiar with nethack, it was the successor to rogue, an early game for text-only consoles. Rogue has become a genre unto itself, continuing to spawn games that attempt to capture its glory. Nethack was basically rogue with a nearly inexhaustible store of replayability that came from the thousands of contributions of users all over the net (hence the name).
Now, Terraria isn't a rogue-like game. It's not turn-based, it's not a straight-up dungeon-dive, it's largely an open-world crafting game like minecraft, and death is not necessarily permanent (there is a hardcore mode).
So why do I say that it's a "worthy game to take nethack's place"? Because it serves the same role in my pantheon of games: a simple game that doesn't require twitch-based reactions (there are some boss fights that come close, but they're mostly strategic rather than tactical) and it has, as of its 1.3 update, a jaw-dropping amount of content! You can play in non-expert mode and reach a satisfying conclusion in a few hours if you're REALLY good (people who have done speed runs have gotten this down to a half hour, but that's not at all practical for anyone who hasn't played it to death, carefully crafted the world options and skipped almost all of the game's content). That gets you to the start of "hard mode" which basically throws you into a completely different scenario where the world fundamentally changes, so many prefer to call that the "end" and that's fine.
But to play out the rest of the game, and to appreciate every little niche of crafting, fishing, building, world events, advanced bosses, etc. You could spend a very long time...
You can pick the game up through Steam directly or from Humble Bundle's storefront.