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.
So it is, thank you! I assumed (wrongly) since it runs on PrBoom it was vanilla compatible.