The most interesting part of this adventure is that it has you exploring a Windling kaer. Windlings are tiny, fairy-like creatures that average about 18 inches tall. That means that a human or ork is going to be approximate as tall as one of their three-story buildings. That's some fun imagery - a band of adventurers wandering through a miniature city like they were some kind of mercenary kaiju.
It becomes less fun when the Windlings were slaughtered by interdimensional bugs and their tiny skeletons litter the ground underfoot, but it's still something that sticks with you. Terror In the Skies would have been a much better adventure if the bulk of its plot were just directly replaced by a list of challenges imposed by the mismatch in scale.
The problem with the Terror In the Skies is that it is a fairly straightforward example of what tvtropes calls "The Macguffin Deliery Service." Monsters are attacking the town! Wow, what luck, there's a wizard who knows exactly where we can find the Tome of Banishment so we can send them back to where they came from! Hey, wait a minute, this creepy underground ruin is not quite as the wizard described. Is anyone else weirded out that the magical lock that seals away the Tome can only be opened by "the purest of heart?" Oh, no, we got the book by solving the ancient riddle, but it turns out the wizard is bad! He's stolen the Tome and is using it to summon more creatures? That's the opposite of what we wanted to do! Okay, he's dead now, let's banish the creatures and restore peace to the town.
If you saw this plot in a video game, you'd think it was basic as hell, but you might forgive it for being made in 1994 (I know, because I forgave Final Fantasy IV for essentially the same sin). In an interactive tabletop rpg, it's just not going to work. The book straight out says, "At some point, Tyrannisis/Rasper-Nor must succeed in snatching the Tome."
Oh, must they? Railroading is bad enough, but this is railroading the PCs into a situation they're really going to hate. The same thing happens near the end of the adventure. Once you kill the wizard and banish the Horror who was controlling him, his airship starts to crash. If the PCs somehow manage to heroically save it from doing so, a local NPC will come by and thank them for donating an airship to the town. Absolutely under no circumstances must the players be allowed to retain control of this airship.
Come on, Terror In the Skies, put at least some effort into understanding player psychology. Your parent gameline puts airships in the core and it's guaranteed that the players have wanted one ever since. So your adventure puts one right in their laps and the closest thing it has to a legitimate owner is that demon-possessed ghoul who was trying to summon a horde of monsters. The right answer to "what happens if the PCs manage to save The Shadow Skulker?" is obviously "I guess your game becomes an airship-centric campaign now."
I suppose what I'm saying is that you can definitely run this adventure in a fairly straightforward way, but the odds are good that you're going to lose the plot before it's all over.
Let's end with something I really liked - the titular "Terror in the Skies" is actually a species of Horror minion called the Rakken, and they've got a pretty neat design. They're these toothy, winged creatures, but they've got arms that shoot flame. These arms swivel on flexible joints and the streams of fire can be used both as weapons and maneuvering thrusters. It's such a bold break from the D&D aesthetic. They're custom-made to be an airship's worst nightmare and as a result they have approximately no fantasy antecedents. It's almost a shame they all get banished at the end.
Ukss Contribuiton: Fuck it, Rakken. The planet Aetheria has sky whales, it could also use a natural predator. Let's keep the legend alive.