This is the first of Roberts' books I've read in which his Tory position is made quite so plain, as he refers very disparagingly to liberals and the left, and their ideas, in a manner bordering at times on glib. Interestingly, however, whilst he's still an ardent Tory, Roberts' views on some issues appear to have evolved since this was written (2003); if you'd only read this book, you might find his later book Napoleon the Great somewhat surprising.
Having said this, there is a slight (other reviews I've read prefer to say an extreme) imbalance, and in more than one way, in that the book not only gives Churchill more column space, ending with a study on how he's been perceived since his passing, but also falls in step with the vast majority of post WWII literature on the two men, in its fulsome praise of Churchill and sometimes crowing dismissals of Hitler.
Roberts says very early in his book that he separates Hitler and Churchill by describing the former as a charismatic leader, and the latter as inspirational. To learn what what he means by that might require that you read this book. I'd highly recommend that you do.