I feel I should probably start by saying that I haven't read the previous book by this author (<I>The Night Circus</i>) for no particular reason despite its popularity - it just never made it onto my TBR pile. So this is my first experience of this author's writing, characterisation and world-building and that will probably have an effect on my views of it as a book.
This is very much a book about books, one where there are secret worlds fought over by different factions who protect or destroy books that are dangerous. Our protagonist once found a door which he could have used to enter these realms and would have been recruited then but chose not to do so. We meet him again when he comes across a mysterious book in the university library that nobody else seems to know about and discovers one of the stories is about him. This leads him on a quest to discover the truth about his own past experience and also what he could have done if he'd only had the courage to embrace his opportunity at the time.
There's plenty going on in this story, most of it described in adjective-heavy detail, and that's both this book's virtue and its curse. If you like that sort of writing, this will probably be a book you'll enjoy, while others will struggle with it because it's just so very wordy in parts. The writing also distracts from the thinness of the characterisation, especially as there are two romantic sub-plots and one of them just <I>happens</i> with no forewarning. It's not massively convincing at all to me that our protagonist will suddenly be in instalove with someone he's met once (and vice versa, though we discover there's been a degree of stalking on the part of the other member of this pairing).
In the end, this book just ends up being another one of those I'm happy to have read but it doesn't make me want to chase up her previous book or desperate to read anything else she's written. There are plenty of other writers doing much stronger work out there at the moment and I'm pretty busy with them and their works...