These are my personal favorites. Note that many of these I enjoyed as a kid so I can't 100% be certain adults will like all of them lol. Some of these are also pretty popular so you may have heard of them already.
NES: Lone Ranger, Super Mario Bros 2, Spy vs Spy
SNES: Earthbound, Pilotwings, Blackthorne, Super Mario World 2: Yoshi's Island, Kirby Superstar
N64: Super Smash Bros, Star Fox 64, Paper Mario
SMS: Didn't play this one much.
Sega CD: Lunar: Silver Star
Sega 32X: Knuckles' Chaotix, but I'm fairly certain it would not be great as an adult.
Sega Saturn: Didn't play this one much either. I remember thinking Nights into Dreams looked really pretty but it felt pretty unrefined, and didn't get into it.
Sega Dreamcast: Only every played Crazy Taxi on this one.
Neo-Geo: Never played it.
PS1: I liked a game called Dragonseeds. FF7 and FF9, and FFT too. Harvest Moon: BTN.
Game Boy / Game Boy Color: Zelda Link's Awakening (DX), Pokemon Games, TMNT: Fall of Foot Clan
GBA: Final Fantasy Tactics Advance, Moto Racer, Mario Kart Super Circuit
DS: Final Fantasy Tactics A2, Mario Kart DS, Professor Layton Series, Phoenix Wright Series
PSP: I didn't ever have one, or emulate one. But if the Sid Meier's Pirates port is any good, it may be worth a shot!
If possible, update us on how the Retroid Flip is!
These are my personal favorites. Note that many of these I enjoyed as a kid so I can't 100% be certain adults will like all of them lol. Some of these are also pretty popular so you may have heard of them already.
If possible, update us on how the Retroid Flip is!