It has been a while since I experienced such a contrast between my expectations of a book and the reality of reading it. I'll still admit freely that the idea of it is a rather brilliant one, in my opinion - it's worth a whole star for me. Otherwise I'd have given it one star.

Gaslamp fantasy is one of my absolute favourites concerning sub-genres. I have had a soft spot for Victorian literature ever since I was 12 or 13 and had learnt English well enough to read - of all things - Arthur Conan Doyle's Sherlock Holmes stories in the original version (which has resulted in a deep affection almost 'akin to love' - to mini-quote from A Scandal in Bohemia - for the detective and the whole canon). I know all of the heroines' 'origin' stories as well as a number of other gothic tales and novels. I even studied English literature for a while... This series should have been for me!

But alas!, it wasn't. It wasn't at all - and, to a certain degree I suppose it was exactly because of what I just explained about myself as a reader.

First of all: the Sherlock Holmes dilemma.
I don't think that modern authors taking up the character(s) and "re-using" them is per se a crime or sacrilege. There are examples where it was done absolutely brilliantly in my opinion (i.e. [b:The House of Silk|11093329|The House of Silk (Horowitz's Holmes, #1)|Anthony Horowitz|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1327877129l/11093329.SY75.jpg|16015218]) - where the author paid attention and hommage to the original material. In this case it felt like the author hadn't even bothered to read more than (perhaps) one of the short stories and decided she would figure the rest out by watching a few recent action movies vaguely based on the books. This usually doesn't work when people give a book presentation at school based on this method, and it didn't work here either.
Another part of the problem is that the main reason for Sherlock Holmes and Dr. Watson to be dragged into this seems to have been to use them as love interests, the first for the allegedly exceptionally logical and clever Mary Jekyll, the second possibly for Beatrice Rappaccini, even if it might be only as a kind of cruel comic relief. While Dr. Watson is known to have an interest in women, Sherlock Holmes is basically famous for not having that, no matter what else he might or might not experience concerning more tender passions. But what was far more irritating to me is that a short research on Wikipedia even would have told the author that Sherlock Holmes would have to be over fourty in her story (because he'd be only available in London again after 1894 due to the small matter of him pretending to be dead after ridding the world of the late Professor Moriarty - but who's counting inconsistencies?), about twice the age of his supposed inamorata who is 21. And while Miss Rappaccini might perhaps be slightly older than that, Dr. Watson also is the older of the two men, and recently widowed... Call me unromantic and closeminded - but even Jane Austen's Mr Knightley would have been a few years closer to Emma than that. This is getting close to Jane Eyre and Mr Rochester - and look how well that went!
Honestly, the group of young women would have been totally fine (and capable of solving this mystery) with hardly any changes to the storyline if Holmes and Watson were just taken out of the equation altogether. They feel obsolete and unnecessary. And I'm also not a fan of love stories without 'chemistry' - there could have been far more interesting and believable combinations from the large group of characters more elementary to the plot (which might have made the book less 'straight as a ruler', though).

Secondly: the time paradox.
This might definitely be a point hardly anyone gets upset over aside from me, I'll own that, and happily. When I read books that are set in (pseudo)historical times, I need to see that reflected in the language as well as the attitude of the characters (aside from, obviously, the 'scenery' in respect to dress codes, technical development, etc.) or I won't be able to 'believe' it. This book is hardly the first case of an author failing there for me - and it isn't the worst case I've seen. But still:
Mary Jekyll, for the first few chapters, wasn't even doing too badly in that respect - until she... met people. Which is a pity because she gets to meet a lot of them. And in this first book of a series at least she's the only character who gets to have more than one to two character traits and thus to feel like more than a stock character - at least that's how it felt to me. It works even less for the rest. It felt as if there was so much attention given to making each character 'quirky' in a different way that giving them depth or a historically believable attitude was somehow forgotten in the process.
The problem is that there are simply too many historically contemporary examples (even outside the 'origin' narrations of the characters) of Victorian social life and etiquette in literature to not notice when an author fails by using the period merely decorationally without managing to get the characters to behave, well, in character.

Thirdly (and finally): the author's distrust in the reader.
Again, this might well be a pet peeve of mine, and mine only. But when an author takes the time to place hints for the reader, maybe even not that subtly at times, to come to the right conclusions - maybe don't have characters state the obvious again, and again, and again, just in case somebody missed all the broad hints because they somehow managed to read with their eyes shut? Also, it doesn't necessarily make the reader believe in a character's brilliance of mind if they only get to a certain explanation/solution half a book after the reader did... An especially prominent example for this were the interjections into the story (which I found quite interesting in the beginning but learnt to be wary of later because they turned into a mixture of 'captain obvious's corner', 'tell-don't show-theatre' and a less humourous version of the 'Mythenmetz'sche Abschweifung').

To sum it all up again, this book wasn't for me, and I will not continue the series for my own peace of mind. And I feel somewhat cheated for that.