I paused midway through to think about it, and settled on "action 3D dungeon crawler." But for some reason "RPG" sounds completely fucking wrong, even though... that's arguably what dungeon crawlers are... right?
The problem is that "RPG" was a very early term that's stuck around, and it's been smeared across a wide variety of influential games. So no, Doom is very obviously not an RPG in the sense of even decade-prior games like Ultima. But the first-person kill-em-all presentation is hard to separate from Akalabeth... an obviously seminal RPG, and the origin of proper dungeon crawlers. And the immediate predecessor to Ultima. It's like we never separated "shooter" from "shoot-em-up."
Yes, if you simplify things down to just combat, then yes, I kind of agree. But the thing that generally separates "RPG" from the rest is whether the player feels like they're playing a role or just playing a game.
Akalabeth gives the player interactive choices (which weapon? Climb the ladder?). The limitations are a mixture of the platform at the time and the skill of the game dev (was built by a teen). But it's obvious that player choice and interaction with the character was a major component here, and the goal is to get the player to the end.
Doom just presents enemies to kill. Yeah, you can change weapons, but it's less in a "character choice" way and more of a "best tool for the job" way. Yeah, it has a character portrait, but I took that to be an indicator of how injured player is, not a RP mechanic. At no point do I consider the character, I just want you press forward to find the next area of monsters (monsters being the goal, not the end or whatever).
If we ignore "shooter" as a category, I think "first person action dungeon crawler" is a good description for Doom, and "first person dungeon crawler RPG" is better for Akalabeth.
Right, but why do you want to get to the end of the map? To see the next one, which hopefully has new monsters to shoot.
The story fits with this. Basically, you're a marine (no name) dropped on a Martian moon to secure a facility. His team is wiped out, so he goes in alone. The facility is apparently working on teleportation, so he battles demons through the facility and into hell. After that, a portal to Earth opens and he enters to fight more demons.
Some notes here:
the Marine is never given a name, and you are never asked to provide one
the goal is to get revenge, not to grow as a person or defeat some evil (though you end up doing that)
there are no character classes, only weapons you find along the way
The character itself is completely forgettable, and there's certainly no progression (you even lose all your weapons at one point). The game seems to go out of its way to distance itself from other games.
In an RPG, the character matters more than pretty much anything else. In Doom, I'm not given any reason to care about the character. Why am I doing all this? Because there's baddies to shoot! That's really all there is to it.
If it were an RPG, it would have some kind of persistent progression (levels, abilities, customized equipment, etc), as probably some kind of internal motivation for the main character (aside from simple revenge).
At the time, I wanted to get to the end because that's how you beat the game. It's like asking why you run to the right in Mario. The enemies there matter about as much as the enemies in Doom, and serve the same purpose in any action game: they're lively obstacles. You don't have to donk every goomba and you don't have to blast every imp.
This is only important because a bunch of mid-00s shooters got it completely wrong. Painkiller in particular was a sequence of kill-em-all rooms. Spawn thirty dudes in a room, kill those thirty dudes, walk to the next room. The enemies were the entire point. There's exactly ten levels like that in all of classic Doom... and that's counting both Final Doom episodes. Only 10 levels out of 132 give one solitary shit about what you kill. Everywhere else - you don't need to shoot anything. It's just fun and useful to do so.
Goals do not tend to be optional. There's a reason the end screen shows a percentage of what you could have done, but that figure has zero mechanical impact. Not even Gauntlet is about the monsters.
Just because you're not obligated to kill the monsters doesn't mean Doom isn't about the monsters. The whole point of Doom is that you're running through a facility and later Hell, both of which are swarming with enemies. You get to the next level to see what else the game is going to throw at you.
And Super Mario is more than just "run right," the point is to save the Princess of the Mushroom people (original game manual PDF). But even that backstory doesn't make Mario an RPG, because the point of the game isn't Mario's story, but the enemies and worlds you go through along the way.
Your mission is to shoot your way through a monster-invested holocaust. Living to tell the tale, if possible.
There's a backstory, but it's pretty short and doesn't really give you a real reason to engage with the character. You're there to get revenge on the monsters who killed your platoon, and that's about it.
And let's look at Akalabeth. There's a backstory, but more importantly there are stats: dexterity, strength, wisdom, and stamina. You get a random start, and can replay the same start by using the same seed. The game is all about the character, not the enemies or the world design. Yeah, it's a dungeon crawler with simple combat, but the whole point is the character.
Therefore Akalabeth is an RPG since that's where the focus is. Doom and Mario aren't, they focus on something else (in Doom, that's monsters, and in Mario, it's getting to the end of the level (there's a timer and reward for getting there quickly).
That's an interesting idea. Maybe I'm misunderstanding your comment or perhaps I just have a poor conception of genres, but, IMO, one of the defining features of dungeon crawlers which seperates them from rpgs is that they're, for the most part, randomly generated. It pains me to say it because it seems rather absurd, but I feel like RPG is actually closer.