This sounds like it would be just my thing, but for some reason, it wasn't.
It's got good writing, concerning both the prose and the plot, but the world-building, while interesting, felt very discombobulated. It tried to explain itself: the Language, the Library, and the fey, creatures of chaos, and dragons, creatures of order, but it wasn't working too well for me.
Also, the writing mostly evokes a Victorian feel to it (though less than the cover would indicate), but the combination of modern technology here and there and modern phrases scattered throughout, while it made sense far as the story was concerned, didn't actually mesh very well in the story. (Congrats if you understood that. Have a cookie.)
As far as Irene and Kai go, I really have very little opinion of them. Kai felt rather one-dimensional and I didn't really...care about Irene? But Vale was pretty cool, and I'd love to see more of him in future books.
As far as the plot goes, I liked the clever bits dealing with Alberich, but I don't quite understand his motivation (they kinda explained it) but even less so how it would work. Kicking myself I didn't write down the page number for this.
To be totally honest, I think I would have liked this best if it had been a completed standalone, rather than at least a six book deal. But I liked this passably well, and am just interested enough to give the next book a go.
This is a bit of the stuff I garnered about the things I wanted more info on:
The Library does what it does for the love of books. Simply to collect books, all the books in all the alternate worlds, and store them and protect them, so that if that book should ever be lost to time or disaster, there will still be a copy to make more from.
The Library exists out of time, so the Librarians are essentially ageless, except when out on book missions, when time passes for them normally.
The Language the fully initiated Librarians use is apparently heard by those who don't understand it in their own language, but with a certain unplaceable accent. The Language is sort-of magic, but it works best when directing something to do what it naturally should be doing, or that it naturally is designed to do (unlocking a door and such). The Language is ever evolving, adding grammar and vocabulary, as most books brought back to the Library are studied and the words or phrases or cool descriptions of the color black are added to the Language. (Or the Language itself evolves from the newly gathered literature???)
Chaos can infect a world, and after the world has been infected and corrupted, then the Fey can manifest to wreck more havoc. But thenDragons are like super chill and creatures of order and often show up to help restore order to the Chaos-corrupted world. Dragons can also take humanoid form.