The very famous diary of Samuel Pepys is one of the few legitimate and most important documents that has survived history and that is narrated from a primary source (Pepys, himself). If you are familiar to French history, Pepys would be the English counterpart in Charles II's England to Le Duc of Saint-Simon in Louis XIV's France. Pepys, however, is an ordinary man who experienced extraordinary chances.
Samuel Pepys was a very fortunate man who occupied an important position as a businessman during a time when England had just lost its "Lord Protector" Oliver Cromwell- A man who overthrew the monarchy but ended up ruling England as if he, himself, were a king.
Pepys apparently took note of the incredible number of changes that were taking place in England, since the rumors of a reconstruction of the throne began to surface. Indeed, during bulk of his writings, the Kingdom of England returned back to its original format bringing Charles II to the throne.
Along with the restoration, a number of radical changes took place in theater, literature, music, and the social life of England.
This being said, Pepys gives us the whole package without giving us things we do not want to know about. He would write about his breakfasts, lunches and dinners, about his relationship with his wife, and even of the beatings he would give his "wretched" servants (out of love and care, as he would state).
Since he is speaking honestly and from a personal point of view, he would even admit to having affairs and even beating his wife "for nagging so much". He placed special emphasis on his loyalty to new regime, provide interesting gossip about the love life of Charles II (a peculiarly promiscuous King), and the drama among the King's mistresses at Court.
In all, Pepys gives us what we could compare to a delicious dish. You get the drama, the gossip, the secrets, and the happenings of a time in history where much was happening in every field from politics to poetry. It is a pleasure to read, and it has enough substance to analyze for many many subtopics and theses.