A somewhat pretentious biography of Rossini which is stronger in its analysis of the music than in its overview of his life. Osborne is clearly writing for the serious opera-lover who already knows about Rossini, his works, and the houses of the time. If you didn't already know that the first two performances of 'Tancredi' had to be prematurely ended due to illness of the lead performer, Osborne won't tell you this directly; he'll tell you in passing as he explains how we know when during the performance it happens, based on what arias the reviews mentioned. He won't explain to you that a particular aria became popular around Europe, instead he'll reference that in passing during another sentence. Essentially, you should already have heard these details over the course of your life; Osborne is merely putting them into sequence for you.
Still, mustn't be churlish. It stands up to reading if you're seeking out particular information or an overview of all the operas that is more substantial than in the New Grove or other focused works on the author.
Make sure you get the 2007 second edition. As Osborne notes in his introduction, it is almost a new book in many ways given the advances of Rossini scholarship in the 25 years since the first edition.