An Introduction to Philosophy by George Stuart Fullerton
Coming back to the question of what has this introduction to philosophy so special, I can only say that from a general perspective much of what philosophy is, was created during antiquity although there are a number of new discoveries in the field and many detailed analyzes of older concepts and ideas. It's a great book and easy to understand. This is also a free/public domain ebook, so another reasons I chose it is for it's 'legality', feel free to share the text to anyone you wish.
Manybooks - I prefer this link because it has many file formats to choose from
Gutenberg - Where it all started