First things first: DCSS is newer than you think (released in 2006) but it's based on games that are old as heck. Its ancestor, Linley's Dungeon Crawl, was released in 1996, which was in turn based on the even older roguelikes (NetHack¹ and its ilk).
I go back to DCSS all the time when I want a straightforwardly difficult game. It's a classic roguelike in that death is permanent, maps are procedurally generated, there are times the RNG is straight up cruel, and you will die a lot. There is no one who has won a classic roguelike who hasn't died trying a thousand times. No one. Zero people.
I'm back on the DCSS train after reluctantly ditching World of Warcraft (suck it, Blizzard), and it's a refreshing challenge after playing a game that showers you with loot for $15 a month. Roguelikes are what truly got me into gaming in the first place, and while they may not always be my individual favourites, they're my home and I'll keep going back until they fall into the sea.
This is the UI for the nerds among us who prefer to ssh² into one of the game servers, but there is a much more user-friendly GUI in the browser. You can also download the game, but unless you have really terrible internet, the browser version is more than fine. There's a bit of a learning curve with the controls, but it's not unreasonable, and there are several shortcuts that don't exist in other roguelikes which go a long way for streamlining gameplay.
Several servers exist; the highest populated one is in the US: crawl.akrasiac.org. Folks in the EU and elsewhere might want to try one of the other servers listed on crawl.develz.org. You can both play a game and watch other people play. (I'm violinsomnia; feel free to watch if you see me in the list!)
Take it for a spin if you don't get attached to your characters and agree that losing is fun.
¹ you can still telnet into nethack.alt.org if you're an especially big nerd like me
² if you don't know what this means, don't worry about it, just use the browser