Common rpg blogosphere wisdom says that heavily scripted adventures are the antithesis of the old school sandbox. In scripted adventures, characters are essentially railroaded from scene to scene and battle to battle, while characters in sandboxes can do anything they want and go anywhere their abilities allow, so long as the pre-existing design of the sandbox allows it. In scripted adventures, change in the world is predetermined by the writer, while change organically occurs in a sandbox as a result of characters' actions.
Gameplay of both scripted modules and old school sandboxes, in addition to some story-driven indie games, over the past few years have convinced me that this is a false distinction.
Last night, we played Death Frost Doom - a seemingly old school sandbox dungeon in many respects that is built for use with a D&D retroclone. The writer, James Raggi IV, exhorted the DM in the intro to be fair according to the way the dungeon was set up and let the characters face the consequences of their actions. The problem was, the dungeon was set up in such a way that the odds were stacked heavily against the characters, and the scenario was generally set up in such a way that there was one very likely conclusion. Indeed, a quick perusal of actual play reviews reveals that many others hit this conclusion upon playing it.
In other words, this "old school" scenario was set up in such a way that the characters were physically free to do what they wanted, but only in the narrow confines of a fairly small physical area. I think there are several ways that Death Frost Doom differs from traditional old school sandboxes, but this aspect remains right on. Given these narrow confines, the characters acted in fairly predictable ways.
On the other hand, we've been playing a heavily scripted Planescape module (Dead Gods) on and off for a while. The scope is epic and crosses several planes. There's a heavy meta-plot built into it. But given some meaty story hooks in addition to just physical ones and the simple lure of treasure, players have made some very unpredictable and wacky decisions around the back story. Needless to say, I've had to heavily modify the module on the fly. In essence, the module has become more of a sandbox than not. And in ways that I never could've predicted in advance.
We've played other more story-driven games more recently as well - like Fading Suns using the Spirit of the Century (SoTC) system. Fading Suns has a crazy amount of source material, and SoTC has mechanics based around story-like attributes of characters, like Haughty Noble (or whatever else one comes up with). Using these mechanics has allowed for unpredictable and organically driven play as well, in ways that just don't emerge in the traditional sandbox.
When I look at all these types of games together as a GM, a conclusion starts to emerge for me: There are lots of ways to allow characters free reign and meaningful choices. Sometimes, an open physical environment works. Sometimes, GM or module-provided story hooks can provoke unpredictable choices that require GM responsiveness and flexibility. Sometimes, explicitly written character traits can serve the same goal. These are all just different tools that the GM and players can bring to bear. Including such tools in game content or game mechanics simply emphasizes and reinforces that aspect of the game. As a GM, I try to select the right tool at the right time because it's not just the content of the module or sandbox that matters; it's also the group, with all their strengths, weaknesses, and mood shifts. It's all about using just the right tool and bringing the cool at just the right time.
And that's really the bottom line for me. I'm not so concerned about remaining true to source material I may have prepped 3 hours before a game as much as providing interesting and fun situations for my players to which I need to respond flexibly. Sometimes, these situations are hard to manage, because a truly open world, with a range of story and character hooks AND mechanics can end up about anywhere. (This is actually my biggest weakness as a GM - that I end up putting myself in situations that are too unpredictable and tough to manage on the fly.)
But it just goes to show: Sometimes the sandbox feels scripted and the script wide open.