One of the interesting things that Skyrim brings to the table is non-linear questing. Or at least less linear questing. In traditional questing-based games like World of Warcraft, the Mass Effect games and Dragon Age: Origins quests are tailored to a certain level range. When you’re in that range you do the quests, otherwise they’re either impossible or provide no useful benefit. In Bioware’s offerings you have some but not much latitude, and the side quests tend to be minimally beneficial. The overall experience is thus fairly linear. Even in quest-based MMOs where there are nominally a lot of quests available, player gravitate towards either the natural or optimal path, and linearity rears its head again.
In Skyrim, and I think this was the intention in Oblivion as well, encounters scale to you. In the latter case it was the entire game world while in Skyrim it’s only certain encounters. But the aggregate effect is that many quests are not gated behind a minimum level. You can go and do what you want, and have at least the illusion of nonlinearity. You can be guided by the questing without being confined either to it or to a particular path therein. And you might in so doing get stomped, but that’s part of the fun and the learning.
Skyrim‘s quest rewards are money and sometimes items. You don’t level by questing; quests provide the impetus to do stuff, but it’s doing stuff that brings actual advancement. Where in a typical MMO the only non-questing means of advancement is grinding, in Skyrim you have other avenues as well, and while I think it’s possible to gimp yourself by leveling via non-combat means like it was in Oblivion, it’s a great deal harder to accomplish, because while the level of any particular task is not stated anywhere in the game, you can adhere to certain principles (like the fact that the lowlands tend to be low level) and muscle your way through a suboptimal build.
I’m not entirely sure how well this could be applied to an MMO, although Guild Wars 2 seems to be promising something closer to it. And in any event it illustrates nicely how questing and the so-called sandbox not only aren’t mutually exclusive even though they have often been in practice, but how the former might be caused to reinforce the latter. Questing isn’t the enemy of the sandbox, linearity is. It’s unfortunate that so few development studios seem to understand that. Bethesda’s not the only one who gets it; TaleWorlds (makers of the Mount & Blade series seem to as well,) and there are others. But among MMO studios, only CCP seems to understand it – and they also understand that while quests can be a component of the sandbox, it can’t be the only one.