This is half-history, half-novel. Or history told like a novel; with extracts from the original material - whole pages of speech from The Secret History, for example - and with picturesque chapter names such as 'Misery and Grandeur of the Nomads'; 'The Tears of Chinggis-Khan'; '"You Have Trampled Underfoot the Head of this Dead Man!"'; '"These Evil-Smelling Mongols"'; 'A Note of High Tragedy: Chinggis Khan and Jamuqa'. I quoted those to tempt you.

It's considered 'popular history'. Grousset has written a huge history of the steppe that doesn't have that 'popular' tag, so don't dismiss him. In my humble, you can do a lot lot worse for a biography on Chinggis. What Grousset does here is give you much of the source material for his life, rather simply without too much imposition of his own - and perhaps that is the best way to start. To make up your own mind.