Book 5 is a very different beast to the previous four books of The Analects in that it features a compilation of Confucius’s opinions on a dozen of his disciples and fourteen contemporary and historical figures.
He certainly doesn’t hold back on his criticisms either, famously castigating his young and rather conceited disciple Zai Yu (宰予) when he found him asleep one day in Chapter X: “Rotten wood cannot be carved; dung walls cannot be troweled. What’s the point of scolding him anymore?”
Even Zigong (子貢), one of his closest and most loyal disciples, is given a frank and bruising appraisal when he asks Confucius what he thinks of him in Chapter IV and receives the response that he is a “vessel” (器/qi) and thus still has a long way to go before becoming a leader (君子/jūnzǐ).
At least Confucius is candid about his own limitations as well, admitting to Zigong in Chapter IX that neither of them are the equal of his protégé Yan Hui (顏回). He also shows quite astonishing courage (or bullheadedness) in his willingness to flout social conventions by marrying his daughter to a convicted criminal called Gongye Chang (公冶長) in Chapter I because he believed him to be innocent. I very much doubt that he consulted the poor girl before making this decision.
To help you understand the context of Confucius’s comments about all the other people featured in Book 5, I have posted a series of pen portraits of them. You can find links to them on the Contemporary Figures and Historical Figures pages.