So I found a thing:
Memoirs of Magic. I'd generally make a thread, but since it is TECHNICALLY a doom WAD, even if it doesn't require the original WADs, I guess it goes here. It's self-contained with a copy of GZDOOM so it's ready to go right after you unpack. Link contains the game trailer and screenshots.
Think Zelda-esque adventure via FPS RPG, right down to the water temple being a fustercluck. While the dungeons need to go in order, the rest of the world is technically non-linear. I've been playing a save for over 6 hours and I've only beaten the second (out of 6) dungeons.
There are seven classes to choose from, each with signature weapons and secondary abilities in addition to magic and alchemy weapons + special ammo you can purchase. Gunslinger is the most doom-esque, while for starters I'd recommend Cleric (free self-healing + b**** food; heavily reliant on melee early on, so buy some weapons asap) knight (agile + early exploration + very useful passive) or warrior (bigger melee hitbox + awesome starter weapons).
A couple of tips and things I wish I knew when I started:
Alchemy points (alchemy weapon ammo) doesn't regenerate from sleeping at an inn. Only potions and nitro jelly recover them.
Some weapons are very useful for some areas and may be worth "sequence breaking" a little for.
You can cook and ? ? ? food! Drop it near a fire or use any heat source.
Some items can only be used by some classes; Books of diplomacy and gun parts to name a few.
Rings may have both good and bad effects. You can also wear multiple rings.
Lockpicking is a rogue only thing, so ignore them otherwise.