A book of wasted potential.
Being the 9th book in a series, readers will already be familiar with the world and its mechanics. Introducing us to international characters is great, but unless their mechanics are totally different (and they're not) you do not need to spend so much time reminding your readers of things you introduced in the first volume. It seriously feels like you could remove 20 pages from this book (or have written 20 more pages of actual plot or character development) if you didn't remind us so many times.
Next, while introducing some new characters is interesting, especially since they may have a different perspective, telling the reader over and over and over and over and over and over and over and over (are you sick of this yet) and over and over and over... that the character is from NYC... well, there's another 10 pages. Not to mention, just how many of your original cast haven't had their stories told. I was glad to see Kanami and her getting some story, even if the focus was Leonardo.
On the whole it wasn't really bad, just imperfect, or rather, still a lesser volume of Log Horizon than many of the previous books. As I can tell there are only a couple more so I'm not sure how introducing Leonardo so late in the game was a good idea, but ya know what -- Touno-sensei has 11 books published and I have none so...