Well, if you paid attention, Doom 1 and 2 were "horror" too (the amount of "creatures from hell", mutilated bodies hanging around as decoration, enemies exploding into giblets of bloody meat etc. are pretty sure giveaways), but the technical limitations of the time prevented them from being as scary as Doom 3.
"Horror" is more than just the setting, it's mainly about the gameplay. Doom 1, 2 and eternal are more action than horror. You have lots of relatively "weak" ennemies to kill. The blood and gore just intensify that "happy trigger" feeling. Rooms are bigs, allowing you to move freely to avoid projectiles.
Doom 3 on the other hand is different; you very rarely have more than one enemy to beat at a time. That single enemy can absolutely shred you if you are not very careful, you have to consider each engagement carefully. The darkness and blood are tuned to intensify that "fear" feeling. Rooms are very small, limiting your ability to dodge, almost to the point of inducing claustrophobia.
Painkiller was released almost as the same time as Doom and was way more action oriented, even tho it contains its fair share of gore.
> "Horror" is more than just the setting, it's mainly about the gameplay. Doom 1, 2 and eternal are more action than horror. You have lots of relatively "weak" ennemies to kill. The blood and gore just intensify that "happy trigger" feeling. Rooms are bigs, allowing you to move freely to avoid projectiles.
It might be just me being overly frightening but I clearly remember 14y old me playing Doom at night with my headphones on and begin scared as fuckin hell when something appeared out of nowhere making guttural noises.
If you know how to strafe, and get to the point that you are habitually doing it almost every second of play, Doom is an action game where you are grossly overpowered compared to your opponents, more or less. To even slow Doom guy down you need tight corridors to cut his maneuverability down and enough enemies to clog him up even so. In open space the only real threat is being plinked away by the undodgeable hit scan weapons; high level play with speedruns involves a lot of managing that and hoping for decent luck. The non-hitscan weapons for them are, to quote a popular Youtuber, super easy, barely an inconvenience, which ironically makes the "weakest" enemies actually the most dangerous in the game in most places.
If you don't know how to strafe, which was very common at the time since we were all new to 3D spaces and even the ones we had used before may not have had a "strafe" option, Doom becomes much more a horror game. As others are saying about how Doom 3 gives you the choice of "seeing" or "shooting", but not both, Doom without strafing gives you the choice of either dodging or shooting, but not both. Shooting becomes a contest of nerves because you're committed for a second or two... to dodge an incoming missile involves turning, then moving. And that move is either "forward", vectoring into the oncoming missile, or backwards, vectoring away but heading away from your field of vision.
I remember both modes now, both playing it back when Doom I was the only release and I played the shareware, and I saw the "strafe" option and had no idea what it was or why I would use it, and playing in later years when strafing was simply part of my 3D "vocabulary" and I did it instinctively. It's almost two different games.
I suspect even at the time, the developers of Doom weren't used to strafing either, and in a weird way it has contributed to its classic status. If they were it would have been balanced much differently.
The same things that make it a gaming classic that people are still playing to this day are also gross violations of the current state of the art of game design and balance... the reader is invited to conclude from that statement whatever they like.
Part of it was that keybindings were still in flux at the time. Strafe actually appeared in Wolfenstein 3D already, but the way you did it was by holding Alt while pressing left/right arrow; you used the arrows without Alt to turn around (and using the mouse to turn was very uncommon back then). The original Doom inherited that.
It wasn't really a good setup even in Wolf3D, but it took some time for the gamers to figure that out, and for those findings to percolate as the defaults in newer games. Even Quake (1) didn't have mouse look + WASD enabled by default. I think part of the inertia was that arrow keys were so ingrained as navigation by design (they're arrows!) that abandoning them just didn't make sense.
Yeah, especially the first time when one of those near-invisible bitey things sneaked up and started gnawing on you, you were in for a pretty good scare...
The later Dooms overdid the platform jumping part. Not that the originals didn't have that, but the trickier jumps were generally only necessary to reach fancier pickups, secrets, and secret levels.
I remember playing around with the Serious Sam level editor. A buddy of mine made a map that was just a small hut in the middle and monster generators scattered over the next hill. Endless mindless hordes of monsters came over that hill and you and your buddies just needed to hold out as long as you could. Pretty amazing for, what, 1999?