And what about games that toe the line between sandbox and themepark, games that offer a bit of sand in their parks or linear questing in their virtual, open worlds? Themeboxes? Sandparks? Let's talk about what makes these MMO mutts so important and so fun to play. I'll list some examples of games that could fit the hybrid definition, but feel free to chime in with more.
The easiest way to define a sandbox is to say, "If I can see it, I can walk to it, kill it, and do what I want with it, without fear of running into a wall of levels or other boundaries." Wurm Online, with its build-where-you-want world of many skills and endless exploration, is a pure sandbox. Second Life could be called one as well.
A themepark is an MMORPG that generally offers class-based play that is based on a linear series of quests through a level-based landscape. We'd call such games themeparks because they take players through a thrill-ride, one that is more or less on rails. This is easily the most popular of the two MMO types right now on sheer numbers alone, possibly because it can require less upfront time, or at least, the possibility of having many choices being made for the player. (Where do I go? What do I do?)
The best way to define a themepark is to say, "If I see it, I might be able to do an epic series of quests that eventually get me there, while also learning about my class and character and role in the world." World of Warcraft is the most well-known themepark, even though the game offers many different ways to play.
RuneScape is a very linear MMO. In fact, the game's age and relatively non-stop development has crafted a world that is absolutely filled to the brim with linear content. A themepark fan can create a very specific type of character and can raise that character's stats and abilities through epic, linear questlines. However, RuneScape blends both the sandbox and themepark by offering many quests that require several different skills. A player who never knew the joys of open-ended character development might find her time being spent raising a few new skills in order to complete a quest. RuneScape is so filled with skills, quests, and events that it is one of the few, pure sandparks out there.
Defiance is a newer and much-less content-rich MMO than RuneScape. In that way, its example is a bit easier to grasp. There a few main questlines in Defiance and players can easily do nothing but complete those quests. Along the way, the player gets points to spend on EGO perks and powers, and the game's FPS-roots means that each new weapon found is basically a new skill that can be switched out with another at any time. I tend to spend my Defiance time in a mix of activities, usually combining the completion of a part of the main questline, jumping into a random event like defending a pack of soldiers against aliens, or joining in with scores of other players to finish off an Arkfall. If I wanted to, I could never complete a quest while I was in-game (other than a few tutorials) and simply stick to open-world content, PvP, and grinding on mobs.
I can already hear what many of you are thinking: Yes, there are many, many different ways to play almost any MMO. There are players who ignore an MMO's standard and seemingly obvious "goals" to walk a unique path. I have always been one of those players, someone who tends to ignore leveling to wander off in the hopes of finding adventure. That's the beautiful thing about MMOs: You can play them how you want to.
Having said that, I cannot ignore how strict some MMOs are and how hard someone would have to fight the game in order to do his own thing within many of these worlds. The awesome thing about sandparks is that they have been designed from the ground up to allow players to play however they choose. So how is that different from a sandbox? A sandbox does allow players to play how they want within the limits of the game's systems. But a sandbox does not always offer the benefits and thrill-ride of a themepark. A themepark might offer some taste of the sandbox's freedom but in general blocks content and growth with level or class requirements. Only when you truly mix the two will you have an MMO from this third category.
In my opinion, the pure sandbox has always been a rarity and will continue to be. Even the most hardcore sandboxes now have to add some sort of linear questlines, goals, or ladders for players who would rather not spend their afternoon trying to figure out how to play. On the other hand, the linear themepark requires many, many hours of development and can result in a bored playerbase who simply followed the linear path to completion.
Perhaps a combination of the two is the best hope for the future?