This is one of the first books I bought on Amazon and, although it took ages to arrive, it was well worth the wait. Unlike any of the other books I've read on the subject, this really gets inside the mind of Stalin and shows you his genius for politics, that has been imitated by the likes of Blair/ Brown.
Most books I've read on the subject focus on Stalin being an evil man and what he did in the purges. Although this does need to be considered, this book (to its credit) focuses on his running of the USSR, and covers 1925 - 1936, which is before the height of the purges and many of his more heinous acts*. It also covers the letters in a objective way, allowing the reader to make their judgements rather than the usual reminders that 'he was an evil man'.
Usefully, the book starts off by going through some of the issues confronting Stalin at the time of these letters, and allows the reader to understand the context of his actions.
The book then goes through his letters year on year up till 1930, and the last chapter is a grouping of letters from 1931-1936. I found the most interesting of these to be the 1929, 1930 ones where Stalin is addressing issues arising from the five year plans. Winston Churchill once said that Stalin was full of 'Good Sense', and these letters let you see why; people who know anything about New Labour's New Deal will see some similarities here (e.g. moving labour to the area of need, and cutting benefits for those who fail to find jobs#).
The other letters are also fascinating (1925 - 1928) and, again, give insight into the mind of Stalin. Molotov appeared to have a very close relationship with Stalin, and Stalin confides in him a great deal. As an example the period 1925-1926 sees a period when Stalin was ill which, if known to an untrusted aide, could have devastated his cause.
Of course, there are downsides to this collection. Firstly, some of the letters get very technical and specific, and commentary isn't provided for every letter. In addition, one feels the book would be more complete with letters covering the whole of Stalin's reign, although whether Molotov disposed of these is not known.
However, to summarise, this book is a fascinating and insightful read and well worth examining if you study the man himself as you will find things in this collection that you won't get elsewhere. I was actually personally recommended this by a History teacher from years back and, suffice to say, it is one of the best recommendations I have ever received!
* - A commenter has pointed out that during the 1925-1936 period there was the Holodomor (where 9-11 million died). The fact the Holodomor doesn't feature at all in the letters (though the Ukraine does), shows the sociopathic nature of Stalin and how his scientific dissections of problems were only possible through his ignoring of human costs... # - This is not intended as a smear, but more to point out to how some of his good-sense policies have been separated from his darker inclinations. It is not without reason that one opponent said of Gordon Brown (at the end of his honeymoon in office) that he had made "a remarkable transformation from Stalin to Mr Bean".