As with all “GM Advice” posts, feel free to take this with a grain of salt.
One of the first things any student of literature or creative writing learns is that an interesting story necessarily involves conflict (man vs. man, man vs. nature, man vs. himself, etc.) This is just as true (if not more true) when it comes to role playing games. If an “adventure” doesn’t involve conflict of some sort, it’s just a tour.
More specifically, in my years of gaming, I can remember a handful of adventures where the GM came up with a “cool idea” and that idea was the adventure. In other words, the PCs were just passive observers of the GM’s cool idea . . . which is seldom as engaging as the GM thinks it will be.
As one example, a GM once ran an “adventure” that involved a town stuck in a time loop. Within the time loop, the Great Destruction had not yet occurred and, as a result, all of the town’s residents repeatedly went about their daily activities, over and over, blissfully unaware of the nightmarish world outside the town’s borders. Is this a “cool” idea? Yes. But is it an “adventure”? No. It could have been a great basis for an adventure . . . but, in this case, the cool idea was the “adventure.”
It didn’t take long for the PCs to realize what was happening in the town and, at that moment, “experience” the GM’s cool idea. But, thereafter, the game was just a series of meaningless conversations with oblivious NPCs who were in complete denial that anything was out of the ordinary. Throughout these conversations and our exploration of the town, the PCs tried to identify their purpose. Were the PCs meant to break the curse and end the time loop? Was there some critical piece of information in the timeless town that would help the PCs solve some other problem? In my opinion, either of these (or anything similar) would have given the PCs and the town a purpose. The cool idea might then have been a memorable backdrop to a memorable adventure.
The same thing can inadvertently happen when a GM designs an elaborate city or other “interesting” location or situation and guides the PCs through the location or situation, describing in detail what they see and experience, without ever making the PCs part of the story. As in the example above, the GM is putting his creativity and/or “world building” skill on display without affording the PCs any significant role. In other words, the GM is setting a scene without presenting the required conflict to make it a story. And players are likely to get bored.
For clarification, the “conflict” need not involve combat. It might be a mystery the PCs need to solve, an NPC the PCs need to persuade, an item or person the PCs need to find, etc. Having such a purpose will encourage the PCs to experience and enjoy the details of the GM’s cool idea or setting without feeling like mere tourists. Ultimately, this will make the game more meaningful, memorable, and enjoyable for everyone.