depends on you're preferences, really. I find N64 games to be very comfy. Super Mario 64, Ocarina of Time, DK64, Quest 64. Jet Force Gemini is exciting, Majora's Mask is cool in a dark way. I'd mostly recommend these if you either have a real system or you have a real controller + usb adapter for emulating. Going older, SNES: Yoshi's Island, Super Mario World, FF4,5,6, Chrono Trigger, Earthbound. Genesis: Sonic 1,2,3, Shining Force. NES: Dragon Warrior 1,2,3,4, FF1,2,3, Startropics, Mother 1. Shatterhand and Super Mario 1,2,3 but they're a little frantic. Gameboy: all three zeldas, Super Mario Land 1,2. maybe SMB Deluxe, Dragon Warrior Monsters, any pokemons. Playstation: Dragon Warrior VII, the Dragon Warrior roguelike, Tony Hawk series, Dave Mirra series, FF7, FF Tactics, Some railroad game (railroad tycoon 2?). PC: basically any DOS shareware era game you played, original Doom, Chex Quest, Jill of the Jungle, that one top-down viking game like zelda I can't remember, Triplane Turmoil, anything on the Windows 95 Monolith CD, minesweeper, solitaire, windows pinball, any point-and-click you played as a kid like Putt Putt, Pajama Sam, that one fox, Grim Fandango. Star Craft: Brood War exclusively against the computer on low speed so you win every game, Command and Conquer series. Mac: That one 3d dinosaur game that came out in the fishtank imac era (not sure if strictly 90s)
not 90s anymore, but for gamecube games: Super Mario Sunshine, Animal Crossing, Zelda Wind Waker, Dave Mirra 2. Playstation 2: Dark Cloud, GTA Series, Tony Hawk Series (stop at wasteland), Smuggler's Run, Dynasty Warriors 2, Enter the Matrix. Xbox: Halo.
so that's a big list of games. basically just play any of those games that fit your genre preferences and/or you played as a kid.