Doom embraced a simple approach to gameplay. Its premise is simple and straightforward, while the story is close to nonexistent. You are a nameless space marine (who colloquially came to be known as the Doom Guy), the only one left alive after a demonic invasion from hell on a UAC (United Aerospace Corporation) base on one of Mars’ moons, Phobos. This is all you need to know to start unloading your ammunition in everything that moves. There are no RPG elements, no friendly NPCs, every creature in Doom is either ready to disintegrate, mutilate or explode you or is already dead. You are humanity’s last hope. This continues the trope that Wolfenstein started of the silent single hero in which all hope rests and this macho strongman model was a common thing for FPS games for a long time. Characters such as Duke Nukem only helped solidify this direction, at least until shooters started being more story oriented and/or adopted a much more liniar model (such as Call of Duty) and took the hardcore macho tone down a notch.
Doom’s story (if we may call it that) spans over 3 episodes with a fourth added with the Ultimate Doom (practically a relaunch of the original with an extra episode). There are five difficulty levels which, in keeping with Wolfenstein fashion are names so as to give you a sense of badassery on the higher ones or chastise you for being a wimp on the lower ones.
The game itself is simple: you have up to 7 weapons you can switch between at any time (provided you have acquired them) and you shoot anything and everything that moves while taking care not to fall prey to melee or ranged attacks. Level design is impeccable and is a staple of the original series. Each level is cohesive and brings enough variety either in its tone, setting or monster set so as not to become repetitive. The atmosphere is gloomy and gives a sense of dread, but also suspense and pumps adrenaline when you least expect it. Dark corridors, trapped rooms and doors that are locked with coloured keycards or opened by a switch hidden somewhere in the level, these all helped build up the challenge and atmosphere of the game.
Each level also has its own soundtrack, most of them drawing heavy inspiration from heavy metal songs and even borrowing riffs and solos for that extra sense of urgency and adrenaline rush. Some, on the other hand, are more toned down and ominous instilling a sense of dread and anticipation that something is about to happen or simply accompanying your though the desolated wasteland that was once the might of the UAC. The first level and its track are already iconic and are instantly recognizable by almost anyone who’s ever touched a mouse and keyboard.
The objective of each level is to find the exit. There is a dynamic automap which helps the player by showing them what parts of the map he has uncovered (and even those he hasn’t if the Computer Map item is found for the respective level). Upon completion there’s a score screen where the player can see how well they’ve done: the percentage of creatures killed, items gathered and secrets discovered, but also the time he took to finish. This gave birth to many gameplay styles and challenges in a time where achievements weren’t a thing. Speedrunning was one of the phenomenons that was spawned in this time. Each episode had a map with key locations corresponding to each level and you get to see which places you’ve visited and which are still to be discovered.
There are 7 weapons in the game and they have corresponding numbers in order of their destructive power. Starting with the basic fist which soon gets replaced by an infinitely satisfying chainsaw which is essentially a close-range blood and gore generator, we move on to the pistol which has low damage and slow firing rate, but is a hitscan weapon so basically hits instantly. It shares ammunition with the machinegun which has a higher firing rate and can keep ranged monster at bay by keeping them in a pain state without the possibility to recover (assuming your aim is good). Every doom player’s favourite weapon, though, is the shotgun which is awesomely effective especially at small range and can take down multiple small enemies because of it’s scatter effect (kinda like a real shotgun). The rocket launcher is perfect for taking out big enemies from a distance. It has huge damage and it’s also AoE, but it can easily also take down the player if they’re not careful and fire it in close quarters.
The last two weapons are reserved for the registered version. These are the plasma rifle which is basically a machinegun with plasma for ammunition and the BFG9000. The plasma rifle isn’t a hitscan weapon, so despite its rate of fire enemies can dodge your projectiles and it also doesn’t have area damage. The latter is the mother of all weapons in videogames and a mainstay in any Doom iteration ever in history, regardless of platform. It also uses plasma as ammunition, but it has huge area damage and a large spread being able to potentially clear a room of enemies.
Doom wouldn’t be Doom without its iconic array of demons and baddies from hell. They are many and varied contributing heavily to the game not feeling repetitive even after several playthroughs. The most basic ones are the zombies, some carrying pistols and some shotguns. Then come the brown and spiky imps who shoot fireballs from afar but also scratch and bite at the player if they get too close. The pinky demons (as they have come to be known) are two-legged muscular demons that run around and try to come close and bite the player. The cacodemons are floating red balls of “Hell, no!” with a single eye and a gaping mouth that shoots fireballs and tries to take a bit out of you if you get to close. Lost souls are flying horned skulls that float around and are fairly easy to take out if they don’t swarm you first, while the Barons of Hell are the bosses of episode 1, bipedal goat demons built like a truck that hit your for a ton of damage and also throw plasma at you.
The supreme creatures in Doom are the Cyberdemon and Spider Mastermind, bosses of the 2nd and 3rd and 4th episodes. The first one is a huge hooved monstrosity with cybernetic parts and a rocket-launcher arm that shoots volleys of 3 rockets every time he spots the player. He is very hard to take down. The spider mastermind is basically a giant cybernetic spider with a huge brain and two cute little tiny hands with a furious hit-scan machinegun mounted up-front for making it practically impossible to dodge its attack without taking cover.
Around the map, the player can encounter various pick-ups. From medkits to armour, new weapons and ammo, but also all kinds of power-ups. The most potent and rare ones include an invulnerability sphere, an invisibility sphere or a mega sphere. Berserk kits give you extra damage with your fists allowing you to kill almost any demon with a single well-placed punch. There are also some items that aid you in your exploration such as the computer map, the goggles that light everything up and the radiation suit which allows the player to walk on sludge, lava and waste without taking damage. There’s also the backpack which upon first pickup doubles the ammo carrying capacity.