There are two things I would note as well - Berdyaev is a fascinating critic and character in the development of Russian philosophy, specifically the religious inspired philosophers that in some way were heirs to Soloviev; Berdyaev operates in the role of a philosophical social commentator as opposed to a primarily theological tradition - in this case he is very different than contemporaries like Sergius Bulgakov or Pavel Florensky. I am most familiar with him through his earlier work, including the Meaning of the Creative Act. This book, of course, echoes Berdyaev's thinking, but he is quite clear in distinguishing his critique from the views of his subject, which makes the book all the more valuable in that it seems to avoid projecting his reading of Dostoevsky into Dostoevsky himself. Of course, others may disagree with this - and perhaps my own reading of both authors is colored by my own interpretation.
However, this certainly weighs on the question of how I would rank Berdyaev's critique of Dostoevsky: while it is not the subtlest discussion I have read, it is one of the simplest and in my view "most correct" readings of the author I have encountered. I would go so far as to suggest that Berdyaev's work deserves a primary place in the secondary literature on Dostoevsky. In fact, I would place it alongside Joseph Frank's monumental intellectual and literary biography as recommended companions to Dostoevsky's novels.
Addendum: I should have mentioned Berdyaev's final assesssment: "So great is the worth of Dostoevsky that to have produced him is by itself sufficient justification for the existence of the Russian people in the world." And that my friends is in my view true.