The whole UK adventures series were, as an Amazon reviewer said, well ahead of their time. Most of them involve a strong railroading, but not much more than the one you get in your usual Pathfinder Adventure Path. You're railroaded okay, but you don't quite feel like it and there's a bit of space for different options if you want to somewhat derail: that's railroading with a leeway, which I will coin as rollercoasting for future debates and blog posts. Now that rollercoasting has become the standard for many players, these adventures shine as brilliant precursors.
In most of them, and When a Star Falls is no exception, you begin somewhere in the wilderness or in a settlement, usually a small town or village, and get to crawl into 2-3 dungeons in a defined order before unveiling an overarching plot and solving it. Usually, these dungeons are original enough to generate an atmosphere that sets the adventure apart from, say, the Caverns of Quasqueton: an abandoned villa, a derro lair that's full of strange machines, a fallen monastery, etc.
The adventure starts in the moors when the player characters stumble across a memory web, a creature that feeds upon memories. Killing it releases all the memories that filled it in a blast, effectively providing the players with enough minimal information to start the adventure.
Messing around: The web could provide the player characters will all the relevant information from the start instead of just giving them starting bits. The adventure would then be all laid bare up front and rely upon their choices as advised in this post. The Spawn of Azathot campaign uses this logic a lot: you've got everything into your hands, and I have 5 adventures ready for you, which one do you choose? The only issue a D&D game, or a “fixed” When a Star Falls adventure would have with this approach is that it would be difficult to scale the adventures according to the character level. What I mean is that the level system implies a progression in adventures that befits more the rollercoaster approach than the wide-open sandbox one. Let me sort this out: okay you don't care about balance, you play OSR, fine. The party goes to some place that's too strong for them to tackle? No big deal, let them flee or die. I'm fine with that. Yet, what will happen is that clever parties will automatically stick with places they belong to level-wise. Hint: it's just the same as rollercoasting. So the level system is a limit here and the rules have to be changed to address it. Make all the places more or less the same in level and cut the progression? Or make level progression ultra-quick in order to let the party explore everything freely? Leave it as it is and have it all fall into place by itself – a.k.a. rollercoasting?
With the memory web, the adventurers learn that a star fell, changing the land as it did. That's the good old cataclysm thing. They then explore the land, and fix what the star has done, helping a new condition to emerge. End of the story.
Messing around: Use the How to Host a Dungeon logic. Create a land, a hexcrawl, a place, a dungeon, whatever. Hit it with a cataclysm. It's like when you launch Godzilla into your Sim City. Change the place accordingly and guess how the inhabitants react. Are the monsters changing? Do some rise in power or go extinct? Create a continent. Hit it with a thousand stars, make a sandbox setting with it. Be careful of the level cap of the zones in the sandbox, you don't want your sandbox to become a rollercoaster.
At the end, you meet derros and machine creatures in a minimal Gnomeregan dungeon.
Messing around: Go further, take the Psychic powers from Stars Without Numbers straight into the campaign, use the radioactive rocks from the Anomalous Subsurface Experiment, Mutant Future or whatever, go for the OSR Megamix.