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!
Seriously. And honestly, even ignoring the super hateful instances, if one server collectively wants to de-federate with another for ANY reason, it is entirely their prerogative. It's funny how many people seem to think that other instances should be FORCED to host others' content, all for their convenience. The level of entitlement there is off the charts.