Final Doom

Coming to Steam alongside the official DOSBox-running releases of the 1993 classic Doom itself is this compilation of sixty-four levels from the cult classic Plutonia Experiment and TNT Evilution campaigns. If you’ve played through the original maps, you’ll already know how these ones work.
They’re good, they’re very pleasingly difficult enough for the Doom veteran, and now they have an official presence on Steam.
Go try ‘em.