It's hard to accept the assertion that the unjust man is 729 times more unhappy than the just man, but generally this book is remarkably topical, politically speaking. Required reading on that count.
Aside from the politics, this book is the origin of Western philosophy and much of Christian theology, and of the still-common idea that there is a superior eternal realm of pure forms of which our mundane existence is but a poor reflection.
I won't go on. This book is where Western civilization comes from. Read it.