While I prefer Dynahack these days for the more luxurious TUI and additional content, Nethack has been one of my favourites from as far back as my Amiga days. Once you realise you can at least try to do anything with anything¹ (use the * wildcard character when asked for an item), the game opens up in ways most RPGs just can’t.

¹ use a wand to write in the dust, train a pet to steal from shops, throw potions at monsters, eat (or refrigerate) slain monsters to gain their abilities, rub lamps just in case, wash the ink off scrolls, use a credit card to unbolt doors…