I'll admit, I was worried about the potential for Nazi subtext. Maybe it's because I've been doing so much (admittedly half-assed) literary criticism for the past couple of years, but I've found my sensitivity to these things to be getting stronger and stronger. Towards the beginning of the blog, I was like "Warhammer 40k does seem to be using a bit of fascist imagery" and now I'm like "is this free-spirited pastoral fantasy based loosely on late 19th/early 20th century Germany actually a back door for an idealized white-supremacist mythology about 'pure European' culture?"
Thankfully, Erika Chappell addresses this head-on in the "Politics" chapter. To paraphrase, "yeah, the potential is there, but please don't." I like that. It's direct, sincere, and conscientious. It makes neither excuses nor apologies, but it does try to head off the worst sorts of harm by drawing a distinction between "fantasy inspired by central Europe" and "fantasy where everyone is white." This is meant to be a game about cool airplanes and the cool people who fly them, and its choice of setting is not incidental (because Germany was a pioneer in early aviation), but neither it is an excuse to indulge in racism.
I also like that this approach is clearly visible in the worldbuilding as well. There isn't just one Himmilgard culture or people, and the idea that there is (or should be) is associated with an antagonist faction, the Goths, that's described as "the worst that people can be" (another, more on-point quote might be "they're fucking nazis.") It may undercut your point a little to include a nazi faction in your explicitly non-nazi "Central European" fantasy, but it does at least remove some ambiguity. If these guys are the nazis, then everyone else is, by implication, not.
Also, there are ethnic groups that intentionally and transparently stand-in for the Jewish and Romani people, and so I suspect that the aim was to try and present a truthful (or maybe truth-ish) translation of how Central Europe actually was, in hopes of forestalling a fascist pseudo-nostalgia. I'm not sure how apt it is to make your Romani stand-ins into airship-dwelling nomadic astronomers who have mastered the art of gliding in magical feathered wingsuits, but the central point - that Himmilgard has always been a diverse crossroads of peoples and the idea that the Himmilvolk are somehow the "true" people of the land is an imperialist project spread by people with a wicked agenda - is well-taken.
As the "Inclusivity" section puts it, "Himmilgard shares these problems with our own world as a mechanism for representation," which is a risky ploy, but a valuable bit of context. This is very much a game that's interested in the perspectives of marginalized people (the Survivor background directly says it's "a metaphor for what if feels like to be a transgender person escaping an unwelcoming or abusive situation") and in order for that to be authentic, there has to be marginalization somewhere. It makes little sense to say, "the culture of pilots in [this] universe is essentially a queer one" if the people left on the ground aren't basically straight. However, I also think the bolded, underlined piece of advice "You shouldn't play out trauma, but you can play out recovery" is useful to keep in mind, and not just for this game in particular.
But enough about politics, what about the true draw of this game - sheer, unabashed airplane nerdery? Sadly, I'm not enough of an airplane nerd to say. This is a Powered by the Apocalypse game, but a lot of the in-flight moves seem to have more to do with physics than they do with drama, and so you can't really go into aerial combat with the same expectations of abstraction as you might have for Apocalypse World, but it's not exactly what I would call a hardcore sim, either. You use range bands and theater of the mind, but there's also precise tracking of your speed and altitude, and it matters what type of engine you're using and what fluid is in your radiator (if you use the optional advanced rules).
My intuition here is that it will all come down to how you feel about the Instrument Panel. It's like a character sheet for your airplane, but with trackers for altitude, airspeed, and g-forces that kind of look gauges you'd see on an early airplane. It's cute an immersive, but also contains a lot of fiddly information. There's a 5x5 grid that tracks modifications to your stats based on how much cargo and fuel you have aboard and there's a designated spot for a picture of your sweetheart. This is a brand of nerdery that is right at the intersection between genre and sim, and if you're on board with it, then learning the intricacies of the combat system will be a delightful adventure.
The on-foot portions of the game are much closer to what I expected from a PbtA game (what, with my two previous examples), but the most interesting part of the system is the way it sets up episodic play with "the Routine."
The Routine is a cyclical pattern of scenes that is driven largely by resource management. When you're on a mission, you accumulate Stress, and too much of it will severely penalize your character. However, removing Stress from your character sheet is the only way to gain experience points, and so the Stress Relief portion of the cycle is vital. But it's not necessarily trivial to relieve Stress. You can indulge vices, spend quality time with loved ones, or have complex personal drama (the book suggests "ill-advised sex") with your fellow pilots, and each of these has their own failure states (becoming addicted to the vice, your loved ones finding out about the ill-advised sex, etc) that may result in you carrying Stress for longer than intended. In the end, missions and stress relief eat into your limited budget and you have to start looking for work so you can start the cycle all over again.
It's a clever way to marry the aircraft stuff with the slice of life stuff and overall it feels like a satisfying structure for a game, but it also puts you pretty deep into the PbtA "play to find out what happens" ideology. If players come in expecting a grand narrative. . . that's still possible, but the system will probably work against them.
Final verdict - Flying Circus is a specific thing, and I'm saying that as a high compliment, not out of any desire to be vague. It's clearly animated by a vision, and that vision is apparent in every detail, and because of that, it could potentially be off-putting to some people. Yet it is that very willingness to alienate that made it such a thrilling thing to experience.
Ukss Contribution: I'm going to go pretty abstract with this one - there's a mythic figure, Sigvird the first king of Gotha, who is an important cultural touchstone for both the Himmilvolk and the Städter peoples. What interests me is that the urban Städters regard him as a demigod, but the rural Himmilvolk see him more as a culture hero. The same person, revered in both, but with two different interpretations. It's interesting to me to see two cultures that are so close and yet so far from one another.
So that's my choice - there will be some figure who plays a prominent role in multiple mythologies, but with significant variance.