I'd call The Secret History of Moscow a collection of stories about people from different times who lived in a secret place under the city of Moscow. It is a qualitative read, but I'd say it's really slow for my taste. The characters are believable, but there's not enough focus on Galina and Yakov. Instead, the book is filled with stories of the characters Galina and Yakov meet in the way.
My rating of this book is 3.5 stars.