When it comes to setting up a sandbox environment for a new campaign, one suggestion you can frequently come across is to begin the process by assembling a pile of your favorite modules and adventures that you always wanted to use or reuse. Arrange them around the map and then look for opportunities to make connections between them, perhaps by doing some reflavoring of NPCs or switching out some monsters.
Having tried that out in the past, this process really does work quite well. You get something pretty solid with a good amount of inviting content quite quickly. But as someone who has a big thing for worlds that are high concept, with distinctive traits that create a specific and unique style, I discovered this approach to come with a considerable drawback. If your planned campaign is a fantasy adventure game, the pool for material to draw from will primarily consist of Dungeons & Dragons releases and third party offshots. The problem with these is that they have been created to either fit neatly into first Greyhawk and later Forgotten Realms, or to fit easily into most people’s campaign. Which are generally quite comparable to Greyhawk or Forgotten Realms. It is what we can today confidently call Generic Fantasy or the Standard Fantasy Setting. Gaming Fantasy has also seen some use as a term in recent years.
That is not to say that such adventure’s aren’t good. Of course, 90% of everything is crap and so are most adventures, but there are some real gems among them that really make you want to run them. In fact, I would say that the best adventures are so good that they can grab you and you can get deeply immersed in them. Which generally is a great thing, but I found it to be a great hindrance when you are trying to create a new campaign with distinctive fresh style.
Of course it completely true that you can always reflavor everything. But my experience over the years has been that it’s always been a real struggle for me. When I want to make great adventures my own, I have to constantly fight them. Making them adjust to my setting instead of my setting adjusting to them. In a way, this gives real credit to those adventures. They get me hooked and immersed just by reading them as a GM. When this happens, the writers certainly did something right.
But it’s not very helpful for me in my effort to create a campaign that feels very different from 15th century western Europe with magic and dragons. So I have increasingly abandoned this approach. Instead I now start by looking at a listing of the key stylistic principles and themes for my planned setting and deduce from that what kinds of adventure locations and antagonist would have the most potential to bring these to life. I still use concepts from some of my favorite modules which I take as the starting point for creating new original content, but no longer use the actual modules themselves. Except for Against the Cult of the Reptile God and The Forgotten Temple of Tharizdun. Those are just too compelling not to use with only cosmetic changes.