The power and pervasiveness of capitalism is inherent in its unmatched ability to absorb reality (and unreality), commoditise it, and then regurgitate it to the public (for a price, of course). Fisher expands on this central thesis, positing that, since the 90s (Fukuyama's infamous 'End of History') the walls of possibility have narrowed considerably to the point where an alternative to capitalism can't be imagined. Furthermore, anything that gets close to critiquing the system is reabsorbed, providing an outlet without any possibility of real consequence. It turns all protest and critique into a fundamentally performative and futile exercise; a postmodern reduction of action to decontextualised inaction.
Although academic in portions (with a heavy emphasis on the work of Deleuze, Lacan via Žižek, and Jameson) one gets the gist of Fisher's main ideas without any need for prior knowledge of these thinkers.
Despite this, the book is strangely uplifting. Fisher concludes his analysis by musing that all it may take is one alternative to capitalism for 'capitalist realism' to begin to unravel. I'd go a step further and posit that the very act of defining capitalist realism may serve the same function. Like a magician performing a trick - when you see the mechanism at play, the illusion is broken.