Topic: Personal favorite that nobody else played

The Darkness 2 may be a little too violent, but it's still an amazing FPS with an amazing plot. It's probably one of in my top 20 FPS's ever, actually.
Henry Hatsworth for the DS is also a great underrated gem. It's easy to dismiss it as one of the many shovelware games that came out for the DS, but it's actually really, really, good.
Remember John Romero's failed FPS game Daikatana? I bet you didn't know it came out for the Game Boy Color as well. It only came out in Europe, and it bears similarities to top down adventure games like the Legend of Zelda. It's one of my favorite GBC games (up there with MGS Ghost Babel), this guy here summed it up pretty well.
I also really enjoyed Suikoden 3, 5, and Tierkreis, Tenchu 1 and 2, the original System Shock, Rayman 2, Beetle Adventure Racing, and Shadow Warrior. I'm not sure if Shadow Warrior really qualifies, but EVERYONE needs to play it. The original and the new one are both amazing.
_{But the original is reaaaaaally racist.} fires nuke "JUST LIKE PEARL HARBOR! HAHAHA!"

PRISM: Light the Way for the DS.
Such an underrated gem. Yes, I'm a sucker for puzzle games.
There's also Asphalt: Urban GT for the DS, too. Fun game once you get the hang of it.

@LavaTwilight: @R_Champ: Yeah, I couldn't find many people who liked it or even heard of it. It wasn't that well advertised around here if I remember correctly so it wasn't surprising to me when I found a new copy for like 10 € like a month after release. This sight just broke my heart.

@Morpheel: That was a good game actually. Sure, I'd play the original X360 VP over it any day of the week but for what it is, it's a good game.

Resonance of Fate - 400k for every region each speaks for itself. It's a shame, because it had really awesome turn-based mechanics. What probably doomed this game was being smashed by being released alongside God of War 3 and Final Fantasy 13.
The Wonderful 101 is a shame too, because the controls are not as awkward as "reviuhwaz" make them to be.
Viewtiful Joe 1 and 2, especially the second now being somewhat rare.
From NES era I say The Fantastic Adventures of Dizzy - it was great and huge adventure game with elements of platformer. NES open world without loading screens or resorting to tricks like map. The only bad thing about it is no save feature, not even a code, so you have to beat it in one sitting. And the game was long, so NES was working 24/7 before it got beaten.
Big Nose the Caveman was also fun to play with great soundtrack to support it. Often dismissed as being "low tier".

Mischief Makers and Astro Boy: Omega Factor. Treasure's two best games, as far as I'm concerned, even though other games overshadowed them. And that's saying something as Treasure's games are cult classics at most in terms of popularity (barring Wario World and maybe the original Gunstar Heroes).

Love love loved Orcs and Elves. I'm still bummed that the sequel wasn't released on DS or 3DS. Hell, I'd even settle for an iOS version (though it wouldn't be anywhere near as good). I also loved the GBA version of The Sims: Bustin' Out which had beautiful visuals and music for the GBA, and its sequels on DS The Urbz and The Sims 2 were also quite good, if not a little underwhelming compared to Bustin' Out. All Sims games released on handhelds after these were utter rubbish. The Sims 3 on 3DS was poor and while The Sims 3: Pets was an improvement, it imposed too many limitations and included too many stupid design choices to make it a playable handheld experience. I would much rather have had a handheld port of The Sims 1 games instead, or a freeroam adventure like The Sims: Bustin' Out was.

While I'm generally opposed to handheld games being released on consoles, I would kill for the early GBA/DS Sims games to be released on Wii U (along with the GBA/DS Pokémon games).

Ghost Trick Phantom Detective - DS
Sakura Wars So Long My Love - Wii

Both are fantastic games that not enough people have played.

@sillygostly: yup Bustin' Out is a great game. I'm glad I found my GBA cartridge. Urbz and Sims 2 (DS) were also pretty good.

I actually preferred the Sims 3 on DS compared to 3ds, for some reason the DS one felt like a better game.

A handheld direct port of the Sims 1 (or 2) would've been a dream come true. But I don't think it'll ever happen. I think the closest thing we'll ever get was the sims 3 on the DS.

I was looking forward to Little King's Story way back when it was still called "Project O" and I adored the final product, but I don't think I've ever met anyone else that has played it. Which is a shame, because LKS is a real gem of a game. I really hope its upcoming PC release will give it another chance to shine and find an audience.

Ranger X is another one. It was one of my favorite Genesis games growing up, but whenever I describe it to anyone I just receive blank stares and I rarely see it on any GEN/MD "Best of" lists.

@RevolverLink: Just played through it this summer and it holds up. Ranger X was one of my favorite Genesis games as a kid.

YES. Gunstar Super Heroes is pretty great too, and despite being a fantastic remake, no one really seems to remember it...

It's made some top 10 lists but rarely do I ever hear people talk about James Bond 007 for Game Boy. It was a surprisingly good action adventure puzzle game.

Not even a joke:

That game is fun. Every Winter Olympics I play it while watching the Games. There are some odd aspects to the game that could have been fixed easily (for example, you can only play as the female Canadian team), but the gameplay itself is really solid. It's the best curling simulator I've come across (admittedly, I've only tried like four, but they usually suck). Yes, I enjoy watching curling for some weird reason.

As a kid though, I had an NES game that nobody I know has even heard of that I absolutely loved. Shingen the Ruler:

It's a turn-based strategy game where you try to take over Japan one province at a time. I didn't have an instruction manual, and I'm not even sure how I got the game, but through hours of trial and error I figured it out and played through it several times. It takes so long to win the whole thing that you often don't even end the game with the character you began with. You have an heir and then have to invest resources into educating and training him in various areas when he is young so he is a better leader when you die. When you die, then you take over as the heir. Besides resource management and keeping everyone happy, the battles themselves were really fun. You had foot soldiers, archers, horseman with different speeds and attacks, and you had to deal with terrain. Fun game, especially when I had nothing but time when I was young to figure it out.

Last Window: The Secret of Cape West (DS, 2010)

A sequel to the also underrated Hotel Dusk. I think it's even better than the original.

@Dave24:
I actually owned resonance of fate at one point but got so overwhelmed with so many games at the time that i ended up just trading it. It never even made it inside my xbox. A shame, I know. Same thing with infinite undiscovery, owned it but never played it.

Quite a lot of games here that I've never heard of. For me it would have to be:
Geometry Wars Galaxies
Mercury Meltdown Revolution
Both for Wii, both great games. Both I never would have heard of it it weren't for Nintendolife reviewing them.

I really really really liked Sonic and the Black Knight. I didn't find the delay in the sword swings to be that detrimental to the experience, and it is probably the best "tunnel" 3d platformer I've ever played, much better than Sonic and the Secret Rings (that game blew), Sonic Adventure, and Crash Bandicoot.

Little King's Story was absolutely fantastic.

Micro Machines 64 is a fun, quirky racer. It has plenty of cars, plenty of tracks, and some nifty power-ups.

Any of the Rush racing games. I love huge ridiculous jumps