I agree with the previous reviewers -- read the other two books first. I found this one first without knowing about the others and it was more enjoyable to revisit after the first two. The fantasy world is original, the stories have pace and are full of intrigue like a political novel, the characters, both Light and Dark, interesting, and the dialogue often funny. Each novel has three stories, each of which starts as a separate story but is in fact complexly intertwined with the previous history.
What gave these novels the edge for me is the setting of modern Russia, with its post-Soviet background, the new and the old still side by side, the Moscow street names, the run down trains... Now I understand something about the proper Russian way to drink vodka and why only Russians can do it right.
The camaraderie between the characters -- more with the Light ones -- is satisfying, the way they manage to have fun even though they're engaged in a permanent secret war with the other side, the occasional uneasy fraternizing with the enemy, all contribute to the enjoyment.
By the way, the blurb "Harry Potter, Russian style" on the book covers does not cut it at all, in my view. If you like fantasy and are looking for something original, dark but not dirty, and which may cause you to search your own heart for the good & evil that is there, then I think you'll be well served.