My complement convinced me to try out Granado Espada recently, and one of the things I noticed while playing was that occasionally another player would walk by. Now, this might seem like a rather silly thing to "notice" since I was playing an MMO, but that's just my point - it struck me that a substantial part of my game experience DIDN'T involve interacting with other people, and even when they popped into view, they usually went on toward whatever monster spawn point they were heading to without stopping to say hello. It was funny, I thought, that I was playing an MMORPG and yet after a full hour of play had only spoken and interacted with NPCs and monsters. And by "funny" I mean weird.
Let's consider another example: Guild Wars. In Guild Wars the only persistent environments are the cities. All explorable areas are instances that contain only the party that set out to explore them. This means that even though there are millions (I don't know what the specific number is) of people who play Guild Wars, and thousands who are online at any given time, throughout most of the time I spend playing, I only see 1-7 other players. Even then, you can fill up the empty slots in your party with henchmen, and in the newer expansions, heroes. What does all of this mean? It means that when I play Guild Wars, I play in a party of me, two friends, and a bunch of NPCs. Despite the supposed "massively multiplayer" nature of the game, my experience, as a player, is that of playing of a 3-person multiplayer game. That's not necessarily a bad thing - I prefer playing with my friends to playing with random 13-year-olds - but it's not really a "massively multiplayer" experience.
But, you object, like I just said, the cities are persistent, and there you can interact with many people at once. This is true. It has also lead to some fun multiplayer experiences, or as I like to call them, "social experiments." I one case, I decided to start running laps around Ascalon city, talking about "staying in shape" while I did it. My friend was amused and joined in, and then a random stranger joined...10 minutes later I had an entourage of 60 players, all running laps around Ascalon city behind me. Some of the people in the back of the line asked "where are we going?" Needless to say, I was pleased with the results. Nonetheless, that totaled about a half-hour of play, and clearly wasn't something the game designers really intended for me to spend my time doing. Outside of district 1 of Ascalon city, which is a 24/7 dance marathon, cities serve two purposes - to gather parties and to customize your character. The thing is, this exists in games that aren't MMOs, as well. Consider Counter-Strike, or just about any RTS game: you join a server where you can create games, customize anything you can control out of game (for example, your "deck" in Age of Empires 3), and chat with people. The only difference is that instead of usernames on the side of the screen, the players in GW have avatars in their giant server rooms.
This brings me to the crux of my post: why is there such a huge push to make games "massively" multiplayer? What happened to making games just multiplayer? The reason I ask is because it seems that most designers working on MMORPGs are under the impression that because they're making an MMO, they're greatly restricted in their options, and that they have to have feature x, y, and z. As I've tried to explain above, however, most of the multiplayer aspects of an MMO are available in games that don't count as being MMOs simply because they don't choose to present themselves as MMOs. In AoE3, you can not only team up with your friends against bots, but by doing so you gain experience and levels which carry over into your future matches and increase your range of abilities. Yet this is not an MMORPG. It's not even an MMORTS. It's just an RTS game.
I think what designers should consider for each and every virtual world they build are 1) just what the unique possibilities of MMOs really are, and 2) how non-MMO games get around the major pitfalls of MMORPGs. I don't have time to go into both these questions in detail, but I'll say something brief about the first one. I think MMOs present two elements that cannot be achieved in single player and "merely multiplayer" games: living economies and co-operative world creation.
Since you have many people sharing (and competing for) the same resources, the value of any item in the game is determined not by design-fiat, but by supply and demand. This is incredibly interesting, and some players are drawn to play MMOs specifically play with the game's economy. That said, most MMORPGs have terribly distorted economies. After the game has been going on for a while, the majority of items are worth either next to nothing or ludicrously large amounts, and even in games with professions and large marketplaces, the richest players are always the high-level players that have completed the highest-level dungeons, who then get to determine the shape of the economy with their enormous expenditures. In other words, economies in MMORPGs are actually very limited, and I'd be willing to bet that almost no MMORPG developers prioritize the economy as one of the most fundamental elements. Rather, they start with combat and quest design, and then get around to worrying about the economy later, when the core mechanics are already decided.
The other unique element that MMOs present is in an even worse position: most MMORPGs lack co-operative world creation altogether. The world that you play in a carefully crafted static world where you can have no impact on anything except your own resources. The static nature of the world is, of course, one of the aspects of MMORPGs that people complain about most often, and is often excused as simply an inescapable consequence of making the game massively multiplayer. I don't understand this excuse at all. As I just said, the potential for co-operative world creation is one of the unique things that MMOs have to offer. Think about all those hundreds of quests in Oblivion, in a world with only one hero running around inside it. Even a dedicated player is only able to explore a fraction of the world, much less the possibility space in the game for different character types, different choices at different turns, etc. If there were a couple hundred, much less a couple of thousand, players running around this world, stealing from people's homes, catching and imprisoning thieves, closing Oblivion gates, etc., you might get an emergent narrative.
The only games that take advantage of these features of MMOs are the ones with little or no gameplay, such as Second Life. Just imagine a game that has an economy and user generated spaces like Second Life, and interesting and dynamic game mechanics to back it up and make the world alive. Then go and play a massively multiplayer game, and prepare to be disappointed. What I want is either a game that's really willing to run with the "MMO" bit and explore the potential of large-scale user interactions, or else a solid RPG that's willing to settle for being "merely multiplayer", so I can play with my friends without having to deal with grind-based gameplay, simplistic quest objectives, and an in-world economy that's in worse trouble than our real world economy is.