It's been a while since I've read a book that tells a full story, start to finish rather than a snippet of a character's story. Faustian bargains and immortality are your broad topics. I highly enjoyed this and could barely put it down.
It does quite a bit of bouncing between past and present, so it can be jarring if you're not paying attention at the start of a chapter.

Schwab writes an EXCELLENT will they/won't they. It's got the just right amount of tension between that and the plot that quite literally fueled me to devour like 70% of the book in one sitting. Plus, THE ROMANCE IS IN THE PAST in reference to the present of the plot. Noting it's in the past, it's obvious that they will but I was so invested in figuring out how they got there (a well written and plausible enemies-to-lovers) and why it went wrong (further cementing the enemies bit).