Despite a whole lot of 'meh', I was compelled to keep reading this book, so I suppose I'm ambivalent, although my over-all feeling is of being unimpressed. I've never been much of a fan of straight murder mysteries, and even though a mysterious codex and sacred relic were pivotal to the plot, the history behind them wasn't, and was only briefly discussed in order to merely identify the object. Which, for me, made this book far less interesting than I thought it would be. The narrative unfolds in a meandering, seemingly disorganized style, sometimes shifting perspectives between characters in the middle of a paragraph, which I found disruptive. As may be standard in a murder mystery, details are withheld and given up over time so that the reader feels led from one conclusion to the next in a somewhat contrived fashion. In the end, the final clue turns out to be something we've repeatedly been told was impossible. Tolkien's characters, however, are interesting and varied, and redeem this otherwise mediocre book. IMHO.
Note: I won an advance reader's copy through the Goodreads First Reads program, which had no influence over my rating or review.