It's no surprise that the Pathfinder Society adventures I write for Paizo Publishing get much more play--and are much more talked about--than the work I do for Run Amok Games or other third-party publishers. This is simply a matter of exposure: Paizo is the largest tabletop RPG company there is, and the Pathfinder Society campaign is their heavily-promoted organized play campaign. I don't have any hard numbers, but I would guess that each of my Pathfinder Society adventures is played thousands of times more frequently than any of my Run Amok Games adventures. And that's quite an honor.

Even more of an honor is to see my Pathfinder Society adventures crop up on Paizo forum posts like "Favorite scenarios to run" and "Best sandbox-y style modules."  My latest two Pathfinder Society adventures, Temple of Empyreal Enlightenment and Severing Ties, have both been listed as "sandbox"-style adventures. If you're unfamiliar with the term, "sandbox" adventures that give the PCs freedom of choice to take any of several paths to their goals or to address challenges in any way they choose; the opposite is linear or "railroad" adventures, where the PCs face encounters in a set A-B-C-D order, without much ability to deviate from that.

I'm certainly not the first adventure writer to say so, but truly "sandbox" adventures are very rare. The types of adventures that get rated as the best "sandbox" adventures--including my own--only give the illusion of choice. 

I want to give some examples, but as a fair warning, vague spoilers are below.

In Temple of Empyreal Enlightenment, the PCs have to go to a location and perform four tasks. They can do the tasks in any order, but they must do all four. While they do, they piece together clues about a local villain. If the PCs don't go confront the villain, the villain picks a fight with the PCs because they've learned too much.

In Severing Ties, the PCs have a two-part mission: first, they have to visit three locations. They can visit them in any order, but they have to go to all three eventually. Second, they have to enter a location and wreck something. Exactly how they wreck the something is up to them, but it has to be wrecked for them to succeed.

I see two common threads here: first, the PCs have a short list of tasks that have to get done, but can perform them in any order. Usually, in my observation, the PCs perform the tasks in exactly the order they were assigned or listed. But that doesn't matter--the players think they have a lot of choice because they could do the tasks in any order, whether they actually mix up the order or not. (Note as an author: if I present the tasks to the GM in the order they're given to the players, that's much easier on the GM, as the players most likely run through them in that specific order anyway.) There isn't a genuine choice to not perform any of the tasks, yet players still consider themselves to be empowered with decision-making authority. This feels "sandboxy" to them.

The second thread is that the PCs are given a task to do but not a lot of information about how to do it. They feel like they can approach the problem from many different angles and they're being empowered to invent solutions rather than follow a preset script. This lets the players feel like they're being creative. There's some illusion here, too, though: if the PCs are told to catalog all the books in a library, it doesn't really matter how inventive they are about dividing up the job: they've still got to catalog all those books to finish their task. If they're told to get Item X from the town baker, they might decide to steal it, or talk him out of it, or otherwise, but they've still got to get Item X. Again, there isn't a genuine choice to not perform these tasks, but the ability to select an approach also feels "sandboxy" to players.

The fact that these adventures aren't true sandboxes doesn't mean the players like them any less; they still seem to be highly regarded adventures. As an author, it's easy to include the simple tricks of (i) presenting a list of tasks, and (ii) giving a specific goal without specific instructions for completion. It's even possible to combine the two: "go accomplish these four goals, and I don't care how you get them done." Players seem to really like that.

At any rate, there are plenty of other great articles out there about sandbox adventures, but I wanted to set forth my own thoughts I've been having as I see my adventures discussed.