2.5 stars.
Law introduces too many philosophers in too little pages in a rather simplified and rushed manner. He presents each philosopher with one or two of their most important ideas in chronological order, but he does not link them to each other. Philosophy as I understand it is a rather broad field with little distinctions between schools or philosophers, and much of these schools of thought are overlapping, and hence it's important to know the interactions of ideas, the arguments for and against those ideas, who supports and who disagrees, and the cultural context in which the particular school of thought originated and flourished, and so on.
I found it rather surprising that the book only introduced one key concept per philosopher, which I felt was insufficient. Descartes' key concept was of course "I think, therefore I am", but I felt that it is important to link that with the Cartesian theater, because after all, it has shaped very drastically the way future thinkers view the mind and reality.
The language and explanation of the concepts were oversimplified. I managed to get through the philosophers I have learned about, but when I was introduced new philosophers I found it impossible to understand their ideas because of the way it was explained.
I wouldn't recommend this to someone looking for a good introduction to philosophy. I have not yet read many books myself, and if anyone has better suggestions, feel free to comment.