Over the last years various MMORPG bloggers have used the terms "sandbox" and "theme-park" to describe games with less or more directions given to the player on what to do. The same concept in earlier years used to be called "world" versus "game" MMORPGs. There are people who would like to live in a virtual world, and there are people who want to play a game. Both are okay, and any given MMORPG to some extent allows both, but there are clearly games that go more in one direction or more in the other.
In the years since the release of World of Warcraft, which is much on the "theme-park" or "game" side, a lot of clones have been made, and so the market is full of "theme-park" or "game" MMORPGs. As that didn't really work out for most game companies, the latest craze is believing that to make a "WoW Killer" you should rather make a "sandbox" MMORPG. Thus all the hype about Everquest Next being the potential savior of the genre.
Unfortunately using the new terminology is leading people astray here. They believe they want a "sandbox", and not a "theme-park". But because the term theme-park is so badly chosen in the first place, and designed as an insult more than a definition, people aren't really aware about the choice there actually is. Using the old terminology of "world" vs. "game" is a LOT clearer, because it shows the inherent conflict between the choices much better.
Look at the description of Everquest Next, and it becomes obvious rather quickly that EQN is *NOT* a pure "world" MMORPG. There are lots and lots of game elements in EQN, and just a slight improvement over the current generation in terms of "world" elements. Everquest Next is still very much a game about killing fantasy monsters to advance in level, about getting to the level cap, about getting the best gear, and all the other standard "theme-park" or "game" elements.
But what is your level in Real Life? You don't have one! Because in a pure "world", without "game" elements, you are not defined by numbers like your level or your strength score. You do have knowledge and skill, you do have possessions which can bring a certain status, but a life in a world isn't possible to put into a few simple numbers. If you wanted to play a "sandbox" or "world" MMORPG, you should play A Tale in the Desert, but most people trying that would complain that there are no character classes, no levels to gain, and no monsters to slay. In short, people *SAY* they want a "sandbox", but in reality they want a game with a bit less hand-holding than current generation MMORPGs offer.
If you have a system of levels and experience points, and a lot of players that can exchange information via the internet, people by trial and error quickly find out the best way to get to whatever top that game offers. Removing hand-holding game design elements like quests can make that optimum path a bit more obscure. But most players have a significant part of "achiever" player type motivation, and will always try to progress as quickly as possible, even if that means optimizing the fun out of the game. The original Everquest had people stay in one spot for weeks, killing the same respawn over and over, because in the absence of quests that was the fastest way to advance. If you want to rather stress the "sandbox" and "world" parts of a MMORPG, you would not just need to remove quests and dungeon finders, you would need to remove leveling, or at least remove the link between game activity and leveling. There is a reason why in EVE Online your skills go up with real time, and not with time played or time spent doing a specific activity: It frees you to do whatever you want instead of optimizing your progress.
There is a good possibility that Everquest Next will be a good MMORPG: The Storybricks based dynamic NPCs have great potential, and there are bunch of other good game ideas. But Everquest Next will by no means be a "sandbox" in which you can do whatever you want. It will be a "game" with a progress on rails, even if those rails might be somewhat better hidden than in current generation games. Because players want that "game", they want the illusion of constant progress and epic treasures. They don't really want to live in a world, they want to mash buttons to kill monsters for xp and gear. A MMORPG without the "G" at the end, something like Second Life, is not what most people want from the genre, regardless of what they are saying.