It's absolutely fascinating to get into the head of a reformer I so admire. Reading his letters to Farel, Melancthon, and the prisoners at Lyons, one sees the human and pastoral sides of Calvin which so are so often denied by his detractors. I can't say that every letter is exactly riveting -- I might say a few are rather boring to read -- but that may actually be a benefit. The reader gets to see something of Calvin's normal life, without imbellishment.
A minister will also find in these letters examples of how Calvin applied the Reformed faith to real-world situations, ranging from small domestic problems to issues of violent persecution. Calvin was certainly no "armchair theologian," and he found much comfort in the doctrines of God's meticulous providence, mercy, and grace.
Linguistically speaking, I'm not qualified to say much about the translation. I don't read french or latin, and so can't make comparisons for accuracy. I can say, however, that the English is a bit awkward at times. A few of the sentences are so long and complex that I had to read them three or four times before I really got the sense of them. Despite that, the book isn't too difficult to read, and actually sounds rather beautiful at times.