The first thing to note about this book is that it was first published in 1889 so it isn't going to be at the cutting edge of modern historiography. However, it has a breeziness of tone that makes it a nice, easy introduction to Walpole.
I picked this up because I've decided - over the next couple of years - to read up on all the Presidents of the USA & Prime Ministers of the UK. No idea why. It just seemed like something worth doing. Plus the 18th century is, pretty much, the biggest blind spot in my historical knowledge of modern England...and Britain. Tudors, Stuarts and the Civil War - Tick. The Nineteenth & Twentieth Centuries - Tick. Georgian England - Nothing, except Blackadder. And the vague idea that every Prince of Wales hated his Kingly father.
This is a very pro-Walpole book. Dismissing various accusations against him in a fine, firm style. I', not sure you'd get away with a book like this now. And I suspect a lot of historiography has passed under the bridge since this was written.
What it has done is make this sound like something I want to know more about and to see if there's a more modern biography worth reading. I mean surely someone has written about Walpole since 1889.