(I got a copy through NetGalley, in exchange for an honest review.)
I really wanted to like this book, all the more since I had loved Daughter of Smoke and Bone, but there's a fine line between "if you liked this, you'll like that as well" and "it's so similar you get to wonder where one ends and the other begins". Not very original. Same comment regarding the comparison with the Shadowhunters series (which isn't so original to start with, but that's another story). As a result, I kept being distracted by the plot turns and character dynamics that were either too close to the one series or too close to the other; in the end, The Girl at Midnight didn't manage to stand on its own for me.
Very obviously, we have Echo/Karou, Caius/Akiva, Ala/Brimstone. Ruby is reminiscent of Madrigal's "friend" in DoSaB. (There's more, but details would lead to spoilers). The relationship between Caius and Dorian is pretty similar to the one between Jace and Alec, including the way it develops when Jasper/Magnus waltzes in. So many common points made it difficult to see the characters for who they could have been, and they remained closer to copies, instead of appearing like people with personalities of their own. Granted, the teasing between Jasper and Dorian was funny, but I couldn't shake off my impression of "hey, I've already seen that...", along with the feeling that relationships in general evolved too quickly in this book.
Relationships: they were all over the place, and not too subtly. I wasn't aware that Echo had a boyfriend until it smacked me in the face, leaving me wondering where that guy came from. (Not to mention that this poor boy seemed to be here just because one love interest wasn't enough and another one was deemed necessary. Basically, he was treated like dirt.) Also, too many mushy descriptions, with our heroine too busy being driven by the love triangle to actually make me feel that she was really involved in the plot—although she does have a fairly important part, one that could have been really good to read about if things hadn't gone too fast.
It's not a long novel, but the pacing was definitely strange: lots of events happening in little time, relationships developing too fast, and yet the story was slow. The world-building wasn't enough to my liking: we get all those nice thresholds, jumping through portals, magic powder, sometimes magical descriptions of places (bonus points for Strasbourg, this city is absolutely lovely—trust me, I lived there for more than 10 years)... but the two races at war, the war itself, didn't feel like "solid". I would've wanted to know so much more about those, how they came to be in such a conflict, the souring relationship between Tanith and Caius, how the Drakharin and Avicen lived... More information in that regard would have allowed me to see the world this story's set in as more strongly grounded. (I guess this would have been less of a problem if I could have fallen back on the characters, only I couldn't, due to the aforementioned similarities. Same goes for the writing: it hadn't the flow of DoSaB's, nor did it bring a really fascinating atmoshpere to Echo's surroundings.)
Conclusion: there were good ideas in this novel, but most often they were too close to stronger, existing ones that it was very difficult to see The Girl at Midnight as a self-contained story.