Distinctions need to be made.
I, too, want a 'huge horde' of monsters crammed in one room.
However, the 'horde mode' I referred to was DOOM 2016's marvelous idea of fun in the form of all entries / exits in a room you just entered magically closing behind and all around you, only to then spawn waves of monsters with an unseen but very scripted and predictable timer between each (with increased difficulty and monster types appearing with each waves). You're going to tell me that the actual human facility we're in acts on its own or on behalf of the hellish invasion and traps you in rooms voluntarily? Sure, it's DOOM, doesn't need to make sense per se. But as a mechanic that load of horse balls had no place in a "DOOM" game. That stuff belongs to other games and the likes of Mass Effect 3 MP. I used to play "horde mode" (Invasion mode) in Unreal Tournament 2004 on custom servers with tons of mods. That stuff was amazing in cooperation with 16+ players in a gigantic room, dealing with waves after waves of monsters.
But that stuff is the bread and butter of Doom 2016. It's essentially interconnected horde mode rooms. Then you eventually get out of the industrial maps and in hell, only to realize that the mechanic is STILL there at that point and keeps on going. It made me quit there, couldn't take it anymore and never touched the game ever again, nor do I ever want to "give it another try". There's absolutely no reasons to play that crap especially when I have my hands on the originals with GZDoom along with Brutal Doom. Now, THAT stuff is Doom gameplay alright. Horde mode rooms that just lock you in by force as a gameplay mechanic is excessively cheap and boring. In the originals and up to Doom 64 and even Doom 3 to some extent I could backtrack, leave a room if I wanted to (whatever the reason may be) during combat and manage my fights better. I don't want some doors and magic walls closing around all around me didcating the flow of the game and the combat. Instead give me good level design and freedom of movement. If you want to give me a challenge don't just spawn 6 monsters with a 5 seconds wait until 7 more spawn, then until 8 more and then 9 more.
Anyway, just wanted to specify what I meant. Wanting a crap ton of monsters crammed in one room is one thing (and happened often enough in the originals; don't worry, I know about and loved it). But in Doom 2016 they're not all there at once. Instead they progressively get peppered on your head a few a time in a locked environment. No thanks.
Just removing that mechanic alone would be a huge step in the right direction for me, for Eternal. But I also hope that Eternal is going to have more than basically just 3 environments to be in and to look at (Doom 2016 has 'interior facility', 'outdoor mars' and 'hell' assets and a few variations and combinations of those here and there; that's about it; it's visually very repetitive and very fast). I'll still keep an eye on it until reviews from normal people come out. And, indeed, bigger... MUCH bigger maps and open ended environments are needed (Doom 2016 is overall a pretty confined game, only some parts of the interiors and outdoors in the Hell levels are more open but aren't that common).