I actually listened to it on the bus and flight home from Brighton a couple of weeks ago! As a fan of pastiches/adaptations focusing on more academic Moriartys, I thought it was creative and enjoyed it with some caveats. Here are some of my (non-spoilery) thoughts:
Pros:
1. The text is surprisingly canonical, with even a few direct quotations and references to canonical details and popular Sherlockian theories that you don't often see in big-name adaptations! Gregson's and Lestrade's rivalry, Porlock, Stationmaster Moriarty, the question of how many James Moriartys (Jameses Moriarty?) there are, the letters to the Times in defense of the professor, and the fact that FINA's plot makes no sense all come up.
2. As much as I am not typically a fan of grimmer Holmes adaptations, I feel like this took both the common fan theories of "what if Mycroft hushed up Col. Moriarty's letters" and "what if Holmes was secretly working for Mycroft the whole time" to their extremes. It also dealt with some of the inconsistencies (for us today) between Holmes's focus on evaluating evidence and grand declarations about innate personality traits.
3. It was very tightly plotted. Details that initially seem extraneous or over-the-top come back later. I wouldn't say it "plays fair" (it isn't that kind of plot), but the return to several random-seeming elements in a new light felt very Holmesian.
Cons:
1. While the text is very Holmesian, the execution (much like Audible's other original Holmes adaptation, Cavan Scott and George Mann's The Voice of Treason) feels very action-heavy, both in terms of the amount of violence (not especially gory in terms of details, but still present), the treatment of characters' injuries, and how far we are supposed to accept Moriarty's actions as desperate and justified. (There is one cliffhanger in particular where it is implied that a particular murder happens where I almost quit listening. I won't spoil except to say that the next episode clears things up, but it still feels like he goes from desperate innocent man to hardened mastermind extremely quickly.)
2. I feel like having the plot totally revolve around the government wanting Moriarty's research and willing to frame him for it was a bit too sudden and one-note. Maybe it's because I'm a big fan of Seven Per-Cent Solution and Michael Kurland's Moriarty novels, but I feel like maybe introducing Holmes as unfairly suspicious of Moriarty and then gradually having Mycroft's people use that to manipulate him might have been more convincing to me than having everyone suddenly convinced he's a murderer and criminal mastermind. The reveal of Watson's role in Holmes's government work and public image also felt like it could have been more subtly developed (although it made for a nice parallel with how Moran is depicted canonically).
3. There were a few moments, especially around legal and criminal justice terminology, that struck me as anachronistic and/or American. Some of this can be explained by incredibly powerful people railroading Moriarty (and the late reveal of one character lying about their nationality), but a few were obvious errors (Moriarty addresses the "ladies and gentlemen of the jury" at his trial and talks about "math" a few times).
Bonus (neither pro nor con, just interesting to me!):
So, it's mentioned early on that Moriarty's fiancée is supposed to be a music student at Durham interested in using mathematics to explain musical structure. This initially struck me as unlikely, given that (1) she's a woman and (2) the whole notion of music as an academic field of study in universities (as opposed to conservatories or through a kind of apprenticeship) is pretty new. But I did some digging in my notes on the history of British musicology and found that Durham offered degrees by examination to "unattached" students until the early 1890s. "Unattached" students in this time often included women (who could not enroll in formal degree programs), but also included students regardless of gender seeking degrees in subjects not formally taught, including music. In fact, multiple prominent British musicologists earned their music degrees by examination at Durham during the 1880s-1890s. I don't know whether or not anyone involved with the production researched this, but having done some work on British musicology a few decades later, I found it interesting!
All in all, I'm glad I listened to this, found it surprisingly more Holmesian than expected, and am always interested in more creative takes on Moriarty. It probably won't be my favorite Moriarty-centric pastiche of the year--I'm particularly looking forward to Kim Newman's "Anno Dracula 1902: The Chances of Anything Coming From Mars" and Robert Harris's The Devil's Blaze--but I'm glad I listened to it instead of just sleeping on my trip home.
Best,
Kristin