I'm finishing up a campaign now. It's been absolutely fantastic, and I highly recommend this game. There are some rough edges, but overall it is maybe my favorite FitD game. It is a staggeringly ambitious game that somehow manages to pull it off. If it worked half as well as it does, it would still be easily one of my favorite games.
These were some of the friction points for my group:
-The layout of the book wasn't always intuitive. For instance, the rules for spending extra time on downtime actions are in the Craft Systems: Coldsleep section rather than in the downtime section, and we never did track down rules for repairing ship harm.
-The logarithmic rules for Scale sometimes led to strange outcomes. E.g. it is better to steal two Scale 1 items with valuable minerals than to steal one Scale 2 item with valuable minerals, despite the Scale 2 item being an order of magnitude larger. (This is a fundamental stumbling block of scale mechanics not unique to A Nocturne; Apocalypse World has the same issue with gang sizes, for instance. And the log scale is a big part of what makes A Nocturne function so well, so I'll forgive some occasional awkwardness.)
-The first downtime was a lot. You need to know how long you are spending on each action, which means you need to know if you are travelling somewhere, and if so how fast, and whether you are going to hop out of coldsleep in the middle of the trip to do a ship score, and if so when. That's a lot of questions to answer all at once. No problem once you are used to it, but a bit overwhelming at the start.
-The ability Jury Rig drastically changes the resource economy, in a way we weren't quite expecting: being able to light-fab literally anything for free once per session just flat out removes one of the major money sinks, and means that manufacturing hypertech items feels a little too easy.
-Some of the rules around the light-fab can be a little confusing or inconsistent.
I want to be clear that these aren't necessarily design flaws, just things that my group in particular tripped over. They can all be easily handled with some common sense and minor houseruling if needed. And the payoff for doing so is amazing. Incredibly evocative playbooks, a fascinating setting, and a game that lets you act on a scale I've never seen before in an rpg while still feeling personal.