I agree with the first reviewer. This collection of lectures, lacking a central theme (how could they), doesn't quite hang together for interest for the modern reader though we may assume that the lecture halls were packed at the time the lectures were delivered.
"No man lives in external truth among salts and acids, but in the warm phantasmagoric chamber of his brain, with the painted windows and storied wall". How true. From On A Certain Blindness In Human Beings.
This is a book with some interesting parts, and occasionally a wonderful few sentences of prose. It could be of interest to anyone interest in the meaning of truth. Mostly it is a straightforward read, and much is enjoyable, but its origin as a series of lectures is apparent and it can be a little dull at times. There are some very interesting concepts explored, but I find it hard to consider this as one of the most important ideas of time to justify its place in Penguins "Great Ideas" series - some of which are truly wondeful. If you are interested in the pragamtic theory of truth, or early twentieth century intellectual oddities, it may be worth a try, otherwise I would give it a miss.