It's not though. it's a terrible book. His takes are incredibly biased and inaccurate, especially in light of modern scholarship.

Is it better than nothing? Yeah, but don't take anything he says seriously, he basically gives shitty crib notes and mocks every philosopher because he's so high on his own supply. And his whole intellectual project, historically, is a bit of a joke and got destroyed by Wittgenstein, which he admitted later in life. Then he turned against Wittgenstein when he started exploring natural language philosophy.