I've always debated how an RPG in the style of the traditional 2D SNES era-esque game would pan out if given multiplayer capability and a really large scope such as in this example. In theory, you're taking the classic nostalgic 2D roleplaying that we all know and love and meshing it with slightly newer idea of mass human interaction and it sounds good, but I dunno if would be as similar in practice as it does in the planning stages. One thing to consider is the visuals of the game. Now, I'm not the type of gamer to defend 3D graphics, exclaiming that they're better than 2D in every way because, for one, I believe that both could suffice depending on the game itself but each respective form has its own benefits over the other. While I feel like such a game could work, it would be made in an open-ended fashion, and I have the sentiment that 3D visuals would be the better alternative. Still, imagine assembling a group of heroes to take down a giant pixelated dragon - sounds pretty epic, right?

Although I am biased towards this style of gameplay, I wouldn't help but to feel a little bit giddy if this ever came to fruitition, and on that note...

The Elder Scrolls series of games do not have a multiplayer option, but the style of gameplay is similar that of your traditional MMO in terms of freedom and, in some ways, the scope of the game world being that they're usually rather large and detailed. Right now, in my spare time, I am jotting down ideas for a puzzle/adventure game but plan to create something similar to the Elder Scrolls games once I finish the first project. I want the game to contain the same style of freedom offered by TES such as a class selection system, quests to undertake, villages to plunder, and a variety of environments to explore and, while there will be a main storyline, you're not neccessarily required to approach it in a linear fashion which has become the essence of the series as a whole. One facet of gameplay that's been causing a ruckus in my mind is how to approach the hero system. So far, I have two different paths to take and I don't know which would bear the better results. Here were some of my ideas.

A hero system where only one hero is chosen:
The various classes aren't set in stone but I'd have the typical RPG classes such as a rogue/scout, cleric, mage, barbarian, bard, necromancer/warlock, etc. Each one would have their own set of field skills to employ out of battle, in addition to their own set of unique skills which are available in the heat of battle. For example, the rogue can stealth and stun, disarm traps, pick locks etc....Don't mention that you've seen these ideas in every other RPG and scoff at me for being so unoriginal, because these ideas are subject to change and are primarily just examples anyhow.

A hero system where a set of heroes is chosen:
And there is the alternative to the one hero system. The player is given several categories of classes, and the option to choose a certain class ffrom each category for their respective battle roles such as healers, damage healers, stat buffers, etc. But, in this case, I probably wouldn't implement the field skills idea since it'd kinda be a little bit too easy to play with.

A set of heroes would be nice for the versatility, and to compensate for their comrades shortcomings. A single hero may have trouble tackling certain spots if they, say, can't heal or remove status effects although potions are still a very viable option and I'd obviously alter the game depending on the system that I decide to go with.

I dunno, though, any thoughts, comments, or ideas?   ​

Haha I remember GRAAL, man that was such a weird game. All I remember doing was memorizing codes to give your character wings and different costumes.

The definition you gave is a bit broad, but I think RO is the closest to what you're trying to describe. There was also a pokemon fan-project at some point, but I don't know how that ended up.