maybe try one or two highly acclaimed game from each genre, subgenre and niche genre:
2D Platformer: Super Mario 3 or Mega Man
3D Platformer: Crash Brandicoot or Mario 64
Beat em Up: Steets of Rage 2 and Alien Vs Predator Arcade
Metroidvania: Super Metroid and Symphony of the Night
Precision Plaformers: Super Meat Boy and Celeste
Puzzle Platformers: The Neverhood and Oddworld
Run and Gun: any Metal Slug and Contra
Shoot em up: Battle Garegga and Ikaruga
Action JRPG: Secret of Mana 3 and Star Ocean 2
Action not anime JRPG: Dark Souls and Dragons Dogma or Nier games
Dialogue Heavy JRPG: Xenogears and Trails series
JRPG: Final Fantasy 6 and Chronno Trigger
Real Time SRPG: Ogre Battle or Dragon Force
Tactical JRPG: any Fire Emblem and Tactics Ogre or Final Fantasy Tactics
Visual Novels: Rance series, Ace Attorney series and Dune 1992
4X Sci FI: Master of Orion and Alpha Centauri
4X: Master of Magic and Civilization 4
Heroes like: Heroes of Might and Magic 3 and Disciples 2 or any King's Bounty or Age of Wonders
God: Dungeon Keeper or Startopia or Black&White or Populous The Beginning
Grand Strategy: any Paradox game
Tactical Turn Based: X-com, Jagged Alliance 2 and Silent Storm
Tactical Wargame: Steel Panthers and Combat Mission
Dungeon Crawler: Wizardry 8 and Might and Magic 6
Dialogue Heavy RPG: Planescape Torment and Disco Elysium
RTWP RPGs: Baldur's Gate 2 and Kotor 2
Turn Based RPG: Fallout and Arcanum
Tacitcal RPG: Temple of the Elemental Evil and Dvinity Original Sin or Knights of the Chalice
One man action RPG: Gothic and Diablo
City Builder: SimCity and any Impression games game
Dwarf Fortress clones: Dwarf Fortress and Rimworld
Management: Football Manager and GearCity
RTS: Starcraft and Warcraft 3 or Red Alet 2 or Total Annihilation
Tactical RT: Myth and Dark Omen
Point and Click: Monkey Island and Indiana Jones and the Fate of Atlantis
3D Point and Click: Grim Fandango and The Longest Journey
Flight Sim Combat: Falcon and Sturmovik
Flight Sim Civilian: Microsoft Flight Simulator or X-Plane
Mecha Sim: Mechwarrior games
Space Sim: Tie Fighter and FreeSpace 2
Space Sim FreeLancer: Privateer and any Elite game
Sub Sim: Silent Hunter 3 and 4 with its mods
Tank Sim: Panzer Elite with Ostpak mod and Battle Tanks: T-34 vs. Tiger
Action Adventure: any Zelda, any GTA
Adventure: Little Big Adventure 2, Outcast
Action Tank Controls: Tomb Raider and Dino Crisis 2
Fighting Game: Street Fighter 2, Mortal Kombat, Tekken, Smash Bros
Hack and Slash: any DMC, any Bayonetta, any 3D Ninja Gaiden, any God of War, God Hand
Stealth: Thief and Metal Gear Solid
Puzzle: Lemmings, The Incredible Machine, DROD
Tank Control Survivor Horror: Resident Evil and Silent Hill
Arcade Military FPS: Call of Duty 2 and Medal of Honor Allied Assault
Commandos clones: Commandos and Desperados
Immersive Sim: Deus Ex and System Shock 2
Linear FPS: Half Life or Unreal
'Realistic' Military FPS: Operation Flashpoint or ARMA 3
Tacitcal Shooter: SWAT 4 and Hidden and Dangerous 2
Old school FPS: Doom or Blood or Quake
Freelancer games: The Ur-Quan Masters, Space Rangers, Starflight, Freelancer, Kenshi, Mount and Blade, Pirates Gold, Pirates of the caribbean with New Horizons mod, Vangers
Roguelike: Stone Soup and DoomRL
Roguelite: Noita and Enter the Gungeon or Hades
Niche games: Sacrifice, Blood Omen, Factorio, Kerbal Space Program, Subnautica, Majesty, Papers Please, Portal, Pathologic, Monster Rancher, Pokemon, Magic Carpet
Those are just some ideas and recommendations, i've not played every game above but i know they're highly praised.