Good hidden gems

Brigane

Epic Pinball (MS-DOS)
Pinball Fantasies (SNES, Game Boy, DOS, Amiga)
Pinball Dreams (SNES, Amiga, Game Boy)
Pinball Dreams II (MS-DOS)
Pinball Mania (MS-DOS, Amiga)
Psycho Pinball (MS-DOS, Sega Genesis)
Extreme Pinball (MS-DOS, PS1)
Absolute Pinball (MS-DOS)
Slam Tilt (Amiga)
Pinball Illusions (Amiga, MS-DOS)
True Pinball (PS1)
Timeshock (MS-DOS, PS1)

Clyde

Jaki Crush (SNES)

blackshadow

not sure what your preferred genre is so ill list a few of my personal favs

Megadrive(im from uk suck it :D )
Crusader of centy/Soleil Action-RPG(basicly the megadrive equiv of zelda not the most amazing game ever but worth a play)
Rocket Knight Adventures (A solid platformer i once owned might play through this when i get chance for nostaliga)
Shadowrun (challanging action-rpg game worth a play or two)
Truxton(this shootemup was the bane of my existance in the old days never did finish it....still havent)

Snes
Terranigma (Badass game the US missed out on as only JAP and PAL saw a release definitly reccomend this)
seiken densetsu 3/Secret of Mana 2 (JAP only has an awesome english patch and i highly reccomend this game)
Axelay (damn good shootemup)

PS1
Future Cop LAPD (good multiplayer/coop mode and has a somewhat challanging singleplayer)
Silent Bomber (run around blow stuff up....love this game)
Persona 2 Innocent Sin (has an english translation patch good rpg)
Gunners Heaven (run n Gun game i rememebr playing a while back)

@Brigane
Respect for suggesting extreme pinball still have the original ps1 disc for that :D

celly

@isack4203 Ninja-50 on GBA. Great game.

Capeman

Alter Ego on NES is a great homebrew.
If you like vintage 2 player games, Fall Down on atari 2600 is intense as 2 player action gets (it's a homebrew also).

I have a post with lots of great hacks and homebrews here - https://retropie.org.uk/forum/topic/8792/big-rom-hacks-homebrew-thread - anything on here with a translation pack would probably qualify as hidden, haha.

PiBoy

SNES - Demon's Crest

PSX - Disruptor, Future Cop LAPD, Harmful Park

hooperre

Whomp Em! My heritage! This and Assassin's Creed 3 are the only games I've played that celebrate Native American culture and history.

beamquaker

BobHarris

@brigane I second Timeshock...it's the table that satisfied my pinball needs for the last 20 years and I still enjoy playing it. Not really a hidden gem though if you know anything about pinball simulations. Also it's a bit of a challenge to get it working properly in Dos. I don't recommend the PS1 version.. doesn't work in the libretro core and also has input lag.

Street fighter III Second impact for FBA is a great hidden gem. Most people are not really familiar with the SFIII games, because when they first came out you could only play them either in the arcade or on the Dreamcast. It does not have a lot of familiar characters from Street Fighter II, but it's a brilliant and beautiful game. For competitive play SFIII Third strike is better, but for solo play I prefer Second impact (it's the only 2D Street fighter game in existence with a true widescreen mode and has better music, sound effects and backgrounds).

PittStone

Gameboy Advance: Alien Hominid

space cadet

Nes mighty bomb jack

Clyde

@pittstone I like the style of Alien Hominid very much. Does the GA version have advantages over the others (Flash, PS2, GameCube, Xbox …), or do you just happen to have that one?

obsidianspider

@clyde You can play it on a Pi? That's an advantage ;)

PittStone

@clyde Yes, the GBA Version can be play'd very easy on a Pi. ;)

PittStone

DOS GAME: Knights of Xentar
(Has English Full Speak or German Full Speak)

Beldar

If you like action platformers, Kick Master is a surprisingly good game. The story is so terrible that it's funny. A princess was kidnapped (very original) and all of the kingdom's knights and warriors have failed to save her. So, they call upon you, the master of kicking things to save the day!

I would rank it up with the later NES Megaman games as far as the fun factor but the controls are a bit loose.

PittStone

DOS Game: Talisman
(Found nothing about it on Youtube. Its a Point'n'Click Adventure with 80's Style Anime FMV's)

Brigane

Jumping Jackson (Amiga, Atari ST)

I remember this being a really fun game while growing up.
Jumpin' Jack'son is a top-down puzzle-platformer about a yellow ball with crazy hair who needs to collect records in order to play his favourite tunes while avoiding the onslaught of evil trumpets, guitars etc.

PittStone

OpenBor:

PittStone

PS2: Cold Fear