The Invisible Library, although published by Tor, reads like a self-published novel, without the strong editorial hand I would have expected from a mass market title. There are excesses of exposition (especially from the villains), it takes forever for the main story to get started, and for the first two thirds of the book, neither of the main characters appear to have any inner life whatsoever. 
 There seems to be a surge in recent Library fiction: this series, the Saint Mary's series (some really troubling relationship issues in those), Jim Hines' Libriomancer (with his sex-addicted nymph character), Rachel Caine's The Great Library (poor worldbuilding, good Harry Potter feel), and the Librarians on TV (yawn). The very best book on libraries for me in recent years was actually the Kingkiller chronicles. Rothfuss *gets* libraries and how they work: the infighting for real power (control the catalog, control the information), the lure and frustration of tracking down information, etc. None of the other titles even came close to the actual mechanics of how amazing and frustrating and mysterious and challenging (and occasionally disgusting -- issues with dust, bugs, etc are real) stored knowledge can be. 
 None of them approached the notion that information can be biased and distorted and that the truth can lie in threads across many sources with various authority and integrity. Rothfuss's story may outwardly be a bildungsroman but at its core lies in the notion that the truth of a story has to be carefully researched, validated, and extracted. He tells one story (the creation war) over and over and over in many forms, just as you'd find in a real library, with the truth distorted and broken and fractured, ready to be reconstructed with hard and detailed consideration. 
 *That* is what library fiction can and should be about. Libraries are not about hunting down books or artifacts because they're valuable (like Indiana Jones, which was not *shock* a good representation of archaeology). Why are these books valuable? It's not just because people want them. Don't beg the question. Outside of Rothfuss, there's no thought, words, or consideration to the weight and value and flaws of knowledge, stories, information, and ideas. Just McGuffins ("an object or device in a movie or a book that serves merely as a trigger for the plot") that people want and never bother to read or if they do, it's just a few paragraphs that instantly offer BIG CLUES(tm). 
 The Invisible Library had modestly engaging world building, and a reasonably interesting mystery. I liked the multiplicity of worlds, and author's construction of the "Language". The steampunk world was fine, although not especially original. The author struggled to decide whether the lead character, Irene, was a James Bond type or an ingenue, leaning far too often to the latter to support the story's progression but including too much of the former to bolster a relatively weak character. Trying to force the lead into the role of a "mentor" with a new student didn't work. It was a mishmash. 
 The book reads like a YA title but includes a horribly awkward scene about sex "partnering". Excised, this would have read like a good book for early teens. Its startling inclusion (plus a few ham-fisted attempts to drop similar innuendo) felt unnecessary in a book that works best with a star struck but smart novice partnered with Sherlock Holmes. The "Great Detective" nonsense was dropped repeatedly in-text, so it's not a leap to figure this out. 
 I disliked the "special chosen one born to the Library" component and the unrealistic relationships, as with her nemesis librarian and her parents. I don't think the Library's mission was well defined and I didn't like that the Library didn't actually seem to do anything but steal books. There was no research, no reading, no hunting down the truth with an overwhelming amount of information. The McGuffin was in book form but could have easily been a letter. 
 I especially didn't like that the library didn't actually do any library-ing, as in researching and reading, and that for the most part there was a system of "action heroes" who had no support staff, proper briefing, etc. The depth of thought into the infrastructure it would take to support these missions was non-existent, what you'd expect from an afternoon kids show. 
 I'm giving this one a 2 star "It was okay". I wavered between "It was okay" and "I liked it" but I didn't *really* like it enough to bump it to 3. Call it 2.5.