I happened to purchase this novel and the author's previous Holmes effort, CHRONICLES OF THE MISSING YEARS, simultaneously. That was fortunate, because if I had purchased and read COTMY first, I would never have purchased another novel by this author, and so would have missed out on this one.
In short, this pastiche has everything that the first novel lacked: plot, vivid characters and characterizations, continual new developments and unexpected incidents. There's a good, scenery-chewing villain, Von Stein, and plenty of frantic action, as various secret agents practice the double- and triple-cross. As in any novel which mixes Holmes into WWI, there's not a lot of opportunity for Holmes to be Holmes--- instead, he's a rather elderly, but still spry action hero.
The novel's only liability is the return of a preposterous character from CHRONICLES, among whose many absurdly exaggerated abilities is that of being in two widely-separated locations at what is apparently the same instant, both timewise and plotwise. It is also a bit disappointing not to have Watson around, and further to be left at novel's end with no clear indication as to the current status of Mycroft Holmes.
If you don't mind some bending of the willow, you'll probably enjoy this adventure of Holmes in the middle East during the height of WWI.