For me it's none other than Nintendo's:

This little game is so damn cool. You can jump between control of anything and anyone on the battlefield, soldiers, tanks, choppers, ships, while giving orders to your troops.

I really don't think Nintendo has taken as much advantage of it as they could but then again their online system kinda sucked.

But now with Wii U, they can take this game to the heights it was meant to be. The online, if done right, would be awesome! Plus, with the controller the game not only has more gameplay possibilities but you can have a nice little local multi-player.

Obviously this game would never be considered 'hardcore'. Too cutesy-like, I guess, but I'm sure if Nintendo puts more effort into it it could become fairly popular with the 'core' and 'casual' market.

So, what game  franchise do you think  has alot more potential than is taken advantage of?

Two words: Pokemon MMO

I was going to say Pokemon Online, too. Everybody knows it would be a phenomenon. Why doesn't Nintendo make it happen?

Also, Custom Robo should have taken over the world. They just did it wrong.

Assassin's Creed. It's not dead yet, but they could have done SO SO SO much more after 2. You make a genius plot device that can get you in ANY time period, and out of 4 games, you decide to make 3 of them in the same era, with the same protagonist, doing the same bloody thing all the time? This could have been one of the most enduring franchises of all time, spanning decades of quality titles. Now, I'm not so sure where the franchise is going to end up. There's still hope for things to turn around though. Let's hope they make it happen.

Also Mass Effect. You make a game with a huge universe with interesting backstory. You make what could have been this generation's Star Wars. You make a good first game with some squandered potential in the gameplay department but nothing we couldn't forgive, a game that despite its shortcomings, managed to feel like an epic space adventure, where your actions affected the world around you. And then you decide to throw all that in a fucking bin and make a corridor shooter so freaking linear in both combat and story structure that it would make Gears seem like a sandbox. Thanks a lot, BioWare. And Mac Walters is still the lead writer for Mass Effect 3. And the gameplay looks exactly like ME2. I can't say I have much hope for this series. Though, I seriously hope I'm wrong.

I would sign up for a Pokemon MMO. I don't care how much a subscription would be

Wave Race - the balance board is crying out for it.
Mario Golf/Tennis - motion plus is crying out for them.

MAG

Mother series.
If used and marketed correctly, we could a have a 1-2 million seller.

Definitely the SOCOM series. It could be one of the funnest online games ever, too bad Zipper is too stupid to realise this.

Resistance. Don't get me wrong, I still think it's a good series, but it could be sooo much better, the alternate history and environments that the game is set in is really interesting and very cool, it's a shame the games play and act like the average shooter. Resistance 3 does look like it's going in the direction that I want it to, but I haven't played it yet so that is based on the first 2 games.

Pokemon. I'm tired of the top-down view and repetitive battle scenes, I want a full 3d huge open world and I want to play as the pokemon in the battles. In terms of scale, think Skyrim. I don't want it to be an MMO, I want it to be a single-player action RPG. It could be amazing, but I actually wouldn't care, since if nintendo were going to do this, the WiiU is the best machine they have for it, and I'm not getting a WiiU. This is why I want Nintendo to be devs and portables only (Although portables won't last long), no more nintendo home consoles. I want Pokemon and Zelda on Playstation 4.

Also, Dead Island. I don't think I need to explain.

That's all I can think of for now.

EDIT: For Pokemon, I want the first 150 or 250, they are by far the best pokemon imo, and too many would probably not work well, I'd rather have 200-ish well thought-out, detailed and balanced pokemon, than 500-ish half-assed pokemon.