First thing that came in to my mind was Gears of War with its specific third person view and hiding behind covers. I don't think it was the first game with that mechanic but the most influential one
Donkey Kong (1981) popularized having different levels in a game to progress a storyline. Until then, you would have the same level over and over with increasing difficulty
Battlefield 1942 always stands out to me as the one that popularized large scale online battles on big maps with vehicles. At the time it was revolutionary in online gaming.
Command & Conquer: Renegade came out around the same time as well, with similar features. I kinda wish that game had a sequel as well.
Another gameplay feature that comes to mind is the exclamation/question mark above NPC characters for quests. I remember it first from WarCraft 3, but I think it really kicked off with World of WarCraft to get adopted by many more games.
Maybe cheating a bit but there are several genres of games that are named after the games that popularized their mechanics such as roguelike/roguelite, souls-like, metroidvania
I think Spyro was the first mainstream game to standardise achievements, you could do random stuff in-game and it gave you a little pop up, carried over to Ratchet and Clank and now every game has official achievements
Kinda wild to see nobody mention System Shock, the game that invented audio logs. It may seem quaint in retrospect, but at the time all shooters were in the vein of Doom, and story in a shooter was considered "like story in porn." System Shock was not only the first to communicate the plot and next steps to the player through found audio logs, but it also filled the player in on side stories and provided characterization to the survivors on Citadel station.
The game recently got a remaster, and despite very few gameplay changes, still holds up really well in 2024. You can really see the bones of later games in it, such as story focused shooters like Bioshock or F.E.A.R. and I'd really recommend it to anyone interested in playing a great retro game.
For first person shooters (mix of first introduced and popularised):
Doom: started and popularised the genre. Also started and popularised rasterized 3d graphics for gaming (though the game itself was still 2d). Also first fps multiplayer and modding
Quake: various game modes (Deathmatch, capture the flag), as well as being the first true 3d fps. Popularised multiplayer and modding.
Team fortress (quake mod): Different specialist characters.
Goldeneye 64: popularized multilayer console fps, taught character size can be a significant advantage/disadvantage, depending on if you got Oddjob or Jaws.
Half-life: started horror fps genre, (mostly) seemless world
CS: customizable loadouts instead of search for guns each time you spawn, more game modes
UT: AI bots
Perfect dark: secondary fire for weapons
Deus ex: rpg fps
Halo: finally figured out a decent controller control scheme (one stick looks, one moves, button for grenades rather than needing to select grenade from list of guns). First fps I remember vehicles in, too.
Battlefield: large scale multiplayer
Socom: fps game that isn't first person, online console multiplayer
Call of duty: using gun sights to aim
Far cry: open world fps
Doom 3: used lighting (or lack thereof) to bring fps horror to a new level.
Crisis: famous for pushing hardware and people caring more about the benchmark results than the game itself (I tried the second one, it was ok but I didn't really get into it)
Call of duty: zombies (and other alternate game modes), kill steaks, online progression (unlocking guns and attachments as you level, prestige levels)
HL2/portal: brought physics and its involvement in fps games to a new level
TF2: f2p, microtransactions (though not predatory or p2w so the game isn't remembered for this)
Borderlands: loot-based fps rpg
Metro 2033: fps survival
Halo reach: custom maps
Destiny: MMORPG FPS
Overwatch: hero-based, and hero roles (dps, tank, healer)
Iirc (edit - apparently incorrect) Halo was the first to use left joystick as forward/backward and left/right strafe; and right joystick as look up/down and pivot left/right.
I even recall articles counting it as a point against the game due to its 'awkward controls' ...but apparently after a tiny learning curve, the entire community/industry got on board.
Rogue for the rogue mechanic.
Progressing in a game as far as you can until you die, then using some form of enhancement mechanic be harder faster better or stronger to go again.
Assassin’s Creed and the Open World Gameplay design. It definitely existed before then, but after AC came out, it felt like every RPG switched to the open world map.
I don’t know what game first came up with it, but Super Mario RPG was the first time I saw timed hits for attack and defense in a JRPG. While the mechanic isn’t exactly ubiquitous it has popped up in a handful of other games over the years and it always reminds me of that game.
Spacewar! was a F2P PvP game with no microtransactions and no battle pass. Although it's hard to quantify exact player numbers (it precedes Steam charts), for a while it was the most played videogame in the world.
Its real-time graphics and multiplayer combat were very influential, and widely copied by many other games.
Jurassic Park: Trespasser invented physics engines in fps games as we know it. The game itself was a buggy mess and a financial disaster. The player's health was shown on the main character's boob for some damn reason. However, they did have the basics of a very good physics engine, and Valve took a lot of their ideas and incorporated it into Half Life 2.
Prince of Persia: realistic animations with weight. also popularized a platformer subgenre, which was called cinematic platformer but unfortunately the life of the subgenre was cut short due to the advent of 3d.
Diablo: ARPG genre, and even more so loot rarity system (especially the four tiers common/rare/epic/legendary) and affixes in loot as well.
Half-Life: a lot of good things, sure, as pointed out by other comments, but I will also never forgive valve for popularizing the game not fucking starting for ages.
Rogue and maybe more so Nethack: roguelike mechanics.
some really obvious ones are Tetris: falling block puzzles and Sokoban: pushing block puzzles.
also now pretty much obsolete but Overwatch: loot boxes. they existed before, but Overwatch made them an industry standard.
Street Fighter 2 popularized and pretty much set to stone what a tournament fighter game should be. Mortal Kombat came first, but its single-player progression was this weird "tower" with some gimmick fights thrown in, like you vs 2.
Thinking about it, I'd say Mortal Kombat popularized the "REALLY fucking cheap sub boss/final boss" that many other fighting games have (looking at you, SNK) - I mean, good luck getting close to Goro in the first place.
I wonder which korean mmo could be considered as the one that de facto popularized pay-to-win as an integral mechanic.
Diablo hands down popularized not only the action RPG genre, but also having enemies as loot mystery boxes. One lucky kill and you could get your hands on a really great piece of equipment. The amount of clones speaks for itself.
I think Gran Turismo popularized the "carreer mode" of racing games.
Crush the Castle inspired Angry Birds and several other games with the same catapult mechanic. Loved that flash game way before Angry Birds was put on the App Store.
WASD + mouse aim in FPS. Wolf3d, Doom1 and Blakestone used the arrow keys, spacebar and Ctrl back in the day. The arrows were turn, not strafe too.
I reckon it was some friends of mine in the 90s in Box Hill, Melbourne, Victoria who were the first to use WASD/mouse aim. Share house above a shop at the end of a tram line.
While some might not consider it a game mechanic I certainly do, as gaming the proceduraly created levels is a core part of certain games, see mapping tactics in Diablo 2 for example as you use knowledge of procedural generation to reduce the time to find and kill bosses!
I'm not 100% sure if factorio was the first, but the devs at Wube certainly perfected the idea and now there's a whole market for the "factory game" genre.
Dune II - basically the grandfather of every RTS game out there (and incidentally very, very different from Dune I): opposing forces, resource collection, tech tree, fog of war, et cetera. Or perhaps it was (not World of) Warcraft, it's been too long and memory gets fuzzy.
Oblivion popularized fucking DLC, holy fucking shit I hate DLC so fucking much I pirated any games that has DLC, I don't mind expansion but DLC can crash and burn in a pile of dogshit
Don’t know if this counts, but Resident Evil 4 killed off the tank controls and single-handedly popularised third person cameras for survival horror games.
I wonder what the source of the RTS conventions was. Ctrl num for making groups. Double press to centre on group. X for scattering units. A to stop them. Pretty sure these predate C&C but the only one before that I can think of is dune.
This might be a little on the side of the main topic but there was always something cool about Crash Bandicoot 100 Apples > 1 Life, and you could grind more to make some levels more forgiving, like semi-adjustable difficulty level based on your previous approach.. And later on — warp zones, you get to choose from a few options so the progression has variation.
Another thing that comes to mind, not sure if a first game to do it, THPS for unlocking movies and later cheat codes, modes and characters for finishing the career. Plus the whole gap marathon for Private Carrera.
Oh, and chanting from Oddword where it had various uses, for saving friends or for changing into enemies, or using special abilities. This definitely was something, because I still remember thinking as a kid, “how cool is that this one ability has so many different uses”.
Im pretty sure the actual, physical Trading card games like MtG and Pokemon gave us all these games with card mechanics in the late 90s/early 2000s.
Culdcept (1997), Baiten Kaitos (2003), Kingdom Hearts - Chain of Memories (2004). Then the card games weren't as popular for a bit, then the digital ones died out.
And then Blizzard released Hearthstone in 2014. I haven't played the other ones to know for sure, but I believe Yu-Gi-Oh Master duels crafting system can directly trace it's roots to it. Trade cards for dust of a specific rarity, dust from 3 can form a new card, Shiny cards give enough dust on their own for any card, etc. .
Another one that comes to mind (that someone can correct me on). Was Uncharted the game that made the “no health bar, but redder screen as you are close to dying” popular?
Dark Souls popularized the stamina meter and the "dropping all your money on death and having to go pick it back up" mechanic. Not to mention spawning a subgenre of similar games like Lies of P and Lords of the Fallen
I feel like Call of Duty 4 modernized and standardized the FPS genre on at least consoles. Every call of duty game still looks and feels exactly the same since CoD4 and every other first person shooter copied it's control scheme because it was so firmly cemented.