Doom II - ★★★★★

What I've learned after playing Doom for a few years is this: Doom is an amazing and strange game. Play other FPS, and similarities between them appear; play Doom, and differences are brought further into relief.

To get a sense of this ask: how fun is it to fight lots of enemies? Quake can handle this... to a point. Push too hard and the encounter devolves into a "scramble fight", where there's too many different independent things going on to read them all. These get exhausting quickly and dilute the individual character of the enemies involved. Arguably this is the "default" state of Quake style FPS, as almost all of its modern successors struggle with this too: Doom 2016, Doom Eternal, Ultrakill, etc.

Doom resists this; its encounters naturally cohere into readable forms. Mixed groups of enemies will tend towards infighting with one another, so that you'll only have to worry about one type attacking you. Projectiles are simple and predictable, allowing you to track and bucket them together in your head compared to e.g. the Quake ogre's erratic bouncing grenades. Enemies easily block each other's firing lines, so you only have to worry about the front ranks.

But the most important aspect is the enemy movement. Enemies are big and slow in Doom, meaning they easily block off your driving lanes to room exits, other enemies, or simply more movement space. They shuffle around unpredictably in the moment, but always move towards you on average. This is the fundamental element of horde combat, which allows the player broad control of how the space available to them evolves, but stays dynamic in the minutiae as individual enemies on the periphery move left in one run, then right in another.

I've been playing a WAD called Pocket Slaughter with small, tuned horde combat encounters, which offers a nice example in Map 20: video. This player starts by sweeping into the side channel, which moves the pinkies and imps away from the left side of the rocket launcher area enough for the player to burrow through with the super shotgun. They hit the switch, then rush to the other side of the map, where the enemy density has cleared up both from movement towards the player over time and with some help from the cyberdemon. They sneak between the hell knights and mancubi, whose infighting has stuck them nearby to clog up the plasma gun area, and tap the switch. The rocket launcher side is cleared up by now, and the player can leave the map (though this person doesn't see the exit for a bit and wanders around) or crush the cyberdemons with a switch and kill all the enemies, which I did in my playthrough.

What I'm trying to convey here is how alien this type of decisionmaking is to other singleplayer FPS. Arguably only Serious Sam compares, but is forced into slow player movement speed; Doom does it while the player is the fastest thing on the map!

And what's even more astonishing is that Doom is at least as good as everyone else at the more traditional, twitchier, dungeon crawler type of classic FPS gameplay. I won't justify this because Romero's expertise is known even now, but just play something like Valiant to see it taken to an extreme of iteration and polish. (And I will tack on the unsupported assertion that the Doom 2 enemy roster is the best in FPS history.)

That iteration is possible because the limitations set on mappers: no room-over-room, limited event triggers, etc. simplify and speed up mapping while still retaining plenty of expressive power. An interesting comparison point is bullet hell shmups (which Doom shares a strange similarity to, gameplay wise...). They're relatively easy to make compared to other games, but still require bespoke coding and art assets. So to get the most out of each game, they drill in on individual depth with scoring systems. Doom mappers don't create experiences that are strictly as deep, but they can instead crank out many different scenarios that are almost as deep, with a large breadth of arrangements that easily explore different areas of the game's state space, while also getting immersive atmosphere at a cheaper cost.

Breadth is a key word there: Doom supports a huge range of aesthetic and mechanical styles, so that breadth translates to individual artistic vision. Valiant's fast and flowing combat gauntlets, Sunder's awe-inspiring and crushing megastructures, Going Down's cruel and joyful whimsy, Abscission's tense horrorscapes, A.L.T.'s surreal silent storytelling. It's an emotional range that's somehow particular to classic Doom's particular mix of adrenaline, mystery, goofiness, and horror, something whose value is felt strongly in its absence (2016/Eternal and others).

Through a confluence of craftsmanship, historical circumstance, and endurance, Doom is the impossible jack of all trades, master of many. It simply stands alone.

(Addendum: I found this very good video, which covers many of these points with more examples: https://www.youtube.com/watch?v=mxbVfa8HJg8)