Two things I like about Grayling: First, he provokes thought. Yes, he makes cogent cases for his views, but seldom ends his essays with "my way or the highway" ultimatums but instead invites the reader to enter profoundly into thinking about whatever topic is at hand. For him, it's all about shaking ideas sufficiently loose so they can be taken in hand, held up to the light, and rotated to view all facets.
And second, he is brief, he is pithy, he leave you wanting more rather than less. Which isn't to exhonerate his occasionally interiminable sentences cluttered to overflowing with pollysyllabic and often Latin words and terms--but at least he doesn't so wear out topics so completely that they are ground into dust.
"Prometheus" is sort of a companion piece to his earlier mini-book, Against All Gods: Six Polemics on Religion and an Essay on Kindness (Oberon Masters), picking up the thread where that one left off. The book is so short that a review of it risks giving away the whole game, so suffice to say that it contains an interesting look at Bertrand Russell and makes a salient case for freeing minds from superstition to pursue reason. He does so with wit and style, as usual. I would suggest, however, that if you consider value to be best obtained on a cents-per-word basis, you might find the work too slight to justify its expense and would perhaps be happier with one of Grayling's longer works...of which I would especially recommend, on similar themes as this one, The Choice of Hercules: Pleasure, Duty and the Good Life in the 21st Century.