Mount and Blade: Warband isn't very well known but is a very enjoyable game to me that should be a lot more popular. I have nearly 300 hours logged onto the game and I haven't regretted a second of it.

River City Ransom is probably one of the NES's most underrated titles. It's got a great fighting and market system with loads of replayability and different strategies to use.

Another one of my favourite's is Spongebob Squarepants: Battle For Bikini Bottom. Yeah, yeah, it sounds stupid but it's actually one of the Gamecube's best, with loads of collectibles and a great hub system, among many others.

IStillSeeTheX : Haha I don't blame you for Spongebob, I'm a sucker for tv show or movie based video games.
If I get a chance I'll check out River City Ransom, sounds like an interesting game.

IStillSeeTheX : I remember that game!  Never owned it, but did check it out from the library and tried to 100% it.  I enjoyed it quite a bit.

As for a game I enjoyed that many others did not, I enjoyed Paper Mario: Sticker Star a good bit.  Yes, there were certain frustrating parts, but I had more fun than frustration.  I replayed it not too long ago, and enjoyed it even more than the first time.  It's an artful experience, but it is quite different from the other Paper Mario titles.

dkmec20 : THIS ONE

https://www.vizzed.com/playonlinegames/game.php?id=87881

It's got some pretty neat game mechanics and no one knows about it unless they're familiar with the show it came from.

Maybe I'm just clueless, but it seems to me that, despite getting a greatest hits version, Jak X: Combat Racing gets nowhere near the recognition that it deserves. In my opinion, it's one of the greatest racing games ever made. I mean, it's incredible even if you don't even like the Jak games. Other than that, there seems to  be a lot of hate for Naruto Uzumaki Chronicles and it's sequel. Sure, the script might be awful, but I still see Resident Evil being cited as the defining game for it's genre.

The game that comes to mind for me is Odyssey: The Legend of Nemesis for the Mac.  Not sure if it's necessarily unpopular as it still has a small fan base that enjoys the game on Mac emulators and the like, but I don't think many have heard of the game.  I know for me this game took up a good portion of my childhood gaming. 

It was an RPG with an open world concept.  The NPCs all had their own daily routines and you could fulfill the story and quests when you wanted to.  One of the nicest touches in the game was the fact that the music played in game was set to classical piano pieces.  

Aerobiz: Supersonic is by far one of my favorite games that very few people have heard of and even fewer have played.

I'm a big fan of "tycoon" style strategy games and this one came along before they got made to the extreme. It's by far one of my favorite old games I've ever played.

I guess you never heard of LEGO Battles? Yes? Oh. Then it shouldn't be here. If you don't know that game, it's a stragety game where you got to complete quests and goals in order to defeat the enemy... with LEGO series from 2009. From Mars Mission, Pirates and Castle, The LEGO group made from those series a storyline, playable from either the good side or the bad side. It's just a great game, which is also playable in multiplayer with 2 or 3 DS systems. Yes, DS. Not 3DS. DS.

If you have the game, too bad you cannot play online. The LEGO group re-made that game once for the LEGO Ninjago series... But they should remake the original one.

I feel Onimusha the first game on the ps2 wasn't known that well. Because back then it was all about KH, KH2,  ffx and all the other popular games. I felt this game wasn't given the recognition it deserves. Because it was and still is a great game to play. I enjoyed playing it a lot because of how the game portrayed in a way. But I really hate how the ending is. I really do. Amazing gameplay and story, but a bitter ending that will just make you angry for on ends. :/

Bulletstorm, its probably the best fps I've ever played

Lego Battles, i remember a friend getting me into this game and we would always battle each other on LAN good times

Metropolis Mania, this game is the greatest man, you are this yellow suit guy with a chalk and you just draw roads and build a city. 

Kingsley's Adventure, released for PSX. A good 3D action platformer. Despite some problems (mostly the camera but I've seen worse, let me tell you), the game itself is a cute and funny tale with decent graphics and a good soundtrack. Some parts of the game were kinda challenging. Plus, it has a bit of Zelda/Metroid mechanics. For example, you can't go to a specific area if you don't have the required item; which, to be perfectly honest, never fails to please me

And speaking of Metroid mechanic, there's a FPS which uses that: Exhumed (a.k.a Powerslave). Ah, killing aliens in Egypt while hearing a great soundtrack played in the background has never been so thrilling. Like Serious Sam ^^

One game that I've always enjoyed, but gets a lot of hate from people because of certain Online Video game reviewers is "TMNT" for NES. I get irritated when people rate down a game because it was difficult. Lots of NES games are difficult. I also disregard the statements regarding it doesn't have a lot of TMNT characters in it, because really, it does. I was a huge fan of the original show and loved the game as well.

A few games that not many people talk about that I really enjoy are as follows (Links to the RGR pages provided)

Guardian Legend - A great mashup of a Futuristic Adventure game as well as a Shmup for NES. Highly underrated. https://www.vizzed.com/play/guardian-legend-the-nes-nintendo-nes-347-game

Clash At Demonhead - A great "Megaman" type action platformer. Basically if you took Bionic Commando and the original Megaman series and combined it, you would have this game. Also the inspiration for the band name on "Scott Pilgrim"

https://www.vizzed.com/play/clash-at-demonhead-nes-nintendo-nes-224-game

Crystalis - A Zelda type action game with a top down perspective. Great game if you enjoy the 2D Zeldas, But has more RPG elements than Zelda. Great music as well. https://www.vizzed.com/play/crystalis-nes-nintendo-nes-202-game

I could post a ton more, but I think that this will suffice for now. Let me know what you think if any of you wind up trying any of the above out!

Triple Play 2001 IDK if it's really all that unknown but it doesn't seem to get talked about that much maybe due to the fact that it's a baseball game from like 15 years ago and it has the rosters from the 1999/2000 season but it's fun to play I like having Pedro Martinez coming off his amazing 1999 season on my team and I like the custom players you can create and the legendary players from the past like Babe Ruth Ty Cobb Willie McCovey etc and also you can play as the Montreal Expos! it's just a fun little game and IDC that it's extremely outdated

Y4123 : I loved that game, way back in the day I believe that was the first baseball game that I ever played an I loved it.

  I love playing Crash Team Racing from Naughty Dog on my PlayStation. It is not as popular as Nintendo's MarioKart but if you've ever actually played both games on their respective real systems, you'd know the one I like has better action, is more playable, is more enjoyable, gives you greater control in races and battles, allows for a wider variation of techniques, a fair set of rules governing which racer gets the most effective power-ups, more ways to use some power-ups, specific ways to counter power-ups with other power-ups or driving techniques and overall, a more engaging experience.

 Mariokart isn't more than a seldom creative spin-off of Nintendo's canon games. With Crash Team Racing, Naughty Dog actually innovated on the material that had been previously created by their company. They made it really interesting and neat to play.

 Mariokart < Crash Team Racing

 P3 

Zero Wing, it's well-known because of "All your base are belong to us" and I think it's quite a good shooter, pretty difficult though.

-Bioshock 2 is my favorite Bioshock. To me, it had the best gameplay and story.

-The Megaman Battle Network series is wonderful.

-I love Manhunt 2.

-This game isn't necessarily "unpopular", but it did recieve a good amount of bad press. I thought The Evil Within was phenomenal, and is definitely one of my favorite games of all time.

IStillSeeTheX :   I would go with the Suikoden series and Valkyrie Profile series.  All very well done and very fun to play

Just about every game in the legend of hero series. I have yet to encounter anyone who has even heard of it before. The unpopularity towards it makes me sad in a way. They seem like really good games.