Sigil 2 - Romero's unofficial 6th DooM episode is out for the 30th anniversary for doom

You can download the free megawad, and the first too. Or you can support them and buy it for a mp3 or costum midi soundtrack.

It is compatible with the original DooM, but made with gzDooM in mind.

I case you didn't know: John Romero is one of the original developers and Co founder of id Software.