This book was my own first introduction to its subject. I agree that it is unsuccessful, on account of it brevity, in summarising the arguments of philosophers. On the other hand, I have often returned to it in preference to Russell (which is just a little too quirky for my liking) and Kenny's much larger history.
As a history it can't really be taken seriously but as an historical sketch it has grown on me and I can't bring myself to be too hard on it. At Penguin prices it is good value and I would not discourage anyone who is curious from using it as a "quick-start" introduction to the subject.