I have now completed reading all three of Tom Robb Smith's book. Child 44 was outstanding. The Secret speech dropped a notch with the poor relationship with his two adopted daughters.
Agent 6 has several items which bothered me. The title is a poor choice as it relates to a minor character. Granted that Agent 6 is the focus of 10 pages near the end. I did not think that he was worthy of the title. This book has more extraneous writing than the others combined. There is a bunch of "stuff" that could have been deleted with absolutely no impact on the storyline. It is like he is padding the book to make it longer.
The ending just doesn't make sense to me. Leo has a good life in America and he has resolution with finding out who committed the murder. After the poor relationship with his daughters in The Secret Speech, why would he go back to Russia just to see his daughters for a short time before he is executed. Leo has no faith in the Russian government so he must have realized the chances of seeing his adopted daughters was minimal.
All that being said, I look forward to Tom Robb Smith's next book. I generally really enjoy his writing style and characters. I do recommend his books. The story lines are out of the ordinary.