There are some really REALLY impressive Doom mods out there. This one is great, but there are some that blow this out of the water.
It's a lot of work to sort through them all, I've not yet found a good place recommending the best ones
Well it really depends on what you're looking for exactly. If you want to tell me your tastes though I could help point you in the right direction. I have a LOT of experience with everything oldschool DOOM.
Thanks skdursh, really appreciated. I've tried and enjoyed Brutal Doom and Brutal Wolfenstein, but I'm really interested in mods that present a whole new game, like this one of course, as well as Rise of the Wool Ball, The Adventures of Square, Aliens Trilogy etc. anything that is really different and stretches the Doom engine's capabilities.
Well you should absolutely check out Blade of Agony https://github.com/Realm667/WolfenDoom. It's one of the most extensive total conversions around and they are just about ready to release the 3rd episode for it. It already has dozens of hours of content and is incredibly well done. Besides that you can find Memoirs of Magic https://strawberryoctii.itch.io/memoirs-of-magic right here on Itch and I also highly recommend most things made by Batandy (Castlevania Simon's Destiny and Golden Souls series https://batandy.itch.io/), Ashes 2063 https://forum.zdoom.org/viewtopic.php?f=19&t=47573 and it's expansion Dead Man Walking https://forum.zdoom.org/viewtopic.php?f=19&t=62707 plus the upcoming sequel Ashes Afterglow (there is a demo which is really good, but it's only a few hours long right now and the full release is just around the corner). There are literally dozens upon dozens of solid TC's out there. I recommend you browse through the ZDoom forums total conversion subforum and see what you find https://forum.zdoom.org/viewforum.php?f=19. Beyond that there is one other total conversion I HIGHLY recommend, but it's a TC of Duke Nukem 3D called AMC TC. It has so much to it I can't even begin to explain it all here, but definitely check out the Moddb page for it when you have a chance. https://www.moddb.com/games/the-amc-tc/ It's a standalone game so all you should need to do is download, extract and start playing.
A few others I recommend:
https://forum.zdoom.org/viewtopic.php?f=19&t=54380 (Inquisitor 3D)