It's an educational if idiosyncratic package. Clark provides straightforward analysis in many cases, like contrasting a pair of contemporaneous masters, or drawing a connection between a technical aspect of painting from different eras. And he does have a sense of humor: one pair of paintings shows a little girl peering around a corner into a landscape from the following century.
This book is good for casual dipping, for instant erudition, and will spark interest in further study of the paintings--and further respect for Kenneth Clark.