This book is based on two lectures given by Marie-Louise von Franz and James Hillman.
Von Franz discusses Jung`s typology of psychological types in general, while Hillman specializes in a whole lecture on the feeling function.
It is advisable to have read Jung's "Psychological types" already, although it is not necessary. However, von Franz would explain the Types in greater detail, adding personal information from her analyitical practice to connect the ideas with experience. All this is very readable and fluently written.
Von Franz would go through the types one by one, explain strengths and difficulties, and also point out the special notion of the inferior function of each type.
HIllman more closely looks at the feeling function, and will give great amounts of additional information about how feeling types behave, what their strengths and difficulties are.
All in all, this book will clearly increase your understanding of Jung's typology dramatically, It will also help to understand what "type" you are, and - last but not least - will help to avoid unnecessary confrontations with other people that stem from not understanding the differences between their typologies.