oh boy there's so many. I could recommend 100s but there's basically 2 places to start - Legacy Wads and Modern Wads.
Legacy wads are the "old school", highly influential ones. rougly from 1993-2007. Hell Revealed 1 & 2. Memento Mori 1 & 2. Scythe 1 & 2. Alien Vendetta. Eternal Doom (not to be confused with the new Doom game). I have great nostalgia for a lot of these but really Hell Revealed 1 & 2 don't really hold up. Memento Mori doesn't really hold up. Out of these I would recommend
Scythe 2. Scythe 2 is still incredible and easily holds up to modern day wads. It's 15 years old this year and is still just as incredible. I also have a very soft spot for Alien Vendetta. Highly influential but harder than the classic Dooms and a little bit jankier and not as cleanly designed as Scythe 2.
Modern Wads get even crazier since some try to stay true to the original Doom games. other include new weapons, enemies, etc. It really depends on what you're looking for. You said classic doom stuff. That's typically what I'm most interested but there's other stuff that's worth highlighting as well.
- Eviternity by Dragonfly & friends. This was released last year and it is possibly the best of all time. a brand new texture pack called OTEX. 6 fantastic episodes each with their own theme. (Medieval, Techbase, Tundra, HydroPlant, Hell, Heaven). my GOTY of 2019.
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Ancient Aliens by skillsaw & friends. a fantastic, trippy blue and purple neon trip through the desert. very classic doom. just absolutely beautiful though. if you enjoyed this one definetely check out his previous work with Valiant and Lunatic.
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Back to Saturn X by esselfortium & friends. This is very classic doomish. new textures and tons of great music by essel and James Paddock. not to difficult as well. This one is a lot of fun.
- Counterattack by Mechadon. This is only a 5 level wad unlike most of the others mentioned here. I hold these in high regard. I absolutely adore how they make you loop back around each other in these gigantic sprawling maps. Very metroidvania feel despite being all classic doom gameplay. Mechadon is also working on
Supplice which looks fucking beautiful.
- Stronghold is a towerdefense styled doom game with waves of monsters. tons of new monsters, weapons, items, turrets, pickups, etc. Much better with friends but still pretty fun solo.
- Skulldash is basically a timetrial/arcadey version of Doom where youre picking up tokens in order to extend the time. Also made by Dragonfly. tons of fun setting new records and great additions in new enemies, weapons and boss fights.
- Total Chaos is a Silient Hill type game with crafting, voice acting, new enemies, textures. It's not really doom. It's GZdoom but it's incredible either way. bone chilling sound design. I'm pretty immune to most horror things but this definitely got to me
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Wolfendoom. What if there was a Wolfenstein game between Wolf 3D and Return released in 1997-1998? This is basically that. We're still waiting on episode 3 but episodes we've got so far are great. better than the new wolfenstein games imo.
The bolded 4 are my favorites - Scythe 2, Eviternity, Ancient Aliens, and Back to Saturn X. But there is also other stuff to check out. sunlust, lilith, kamasutra, hellbound, hellforged, shrine, good morning phobos, speed of doom, preacher, rekkr, sunder, swift death, winter's fury, struggle, ESP, etc. so so so so so so many to recommend. But I don't want to ramble on too much. (:
The cacoawards are indeed overwhelming but I highly recommend checking out this article about 25 years of doom modding. It covers a lot of the wads I talked about and goes in depth about influences and whatnot.
