Don't believe the detractors, this is one of the most far sighted, visionary and original pieces of SF to emerge in the past 20 years.
Accelerando takes the reader into a future not so far from our own in subjective time (most of the book is set less than 100 years in the future) but through, as another reviewer said, tackling the idea of the technological singularity head on Stross delves into a world which by its very definition is at an incomprehensible remove from that of the reader. His masterstroke lies in sustaining this sense of alien change whilst keeping enough of a thread of understandable humanity runnning through the story.
Be prepared to have to re-read passages and to take the time to do a bit of side research on his ideas, technical details and vocabulary, but prepare also to be rewarded by a true 'sense of wonder', that of standing teetering on the brink of a fathomless gulf of experience over and above and beyond your ken . . .
Woven through these towering ideas there is a hugely powerful thread of character, for those who read carefully enough . . . the Macx family with its forks, twists and disfunctions is presented, in a way, as a reflection of the future shattering of human values as we currently understand them. And, whilst trying not to give anything away, the thread which ties all this together is a character who I think is one of the most believably, spine chillingly developed images of an alien intelligence yet written.
My caveat would be that this is not a book for those who are just starting to delve into sci-fi. There are both explicit references to and subtle echoes of many previous works of SF. Some obvious authors (again, as others have said) who have influenced Stross and the genre he writes in are William Gibson, Vernor Vinge, Neal Stephenson and Ian M. Banks, and these all offer their own delights which are, for the most part, easier to tackle and digest than Accelerando.
But if you put the effort into understanding it, the vision, innovation and control of ideas in Stross' writing will leave you reeling.
Addendum: If the book's world were true the Amazon sentient class action lawsuits might come knocking at my door for this - the full text of Accelerando has been made available with full permission of author and publisher at accelerando dot org for free download. Good to see Stross backing the convictions on drm expressed in the book for real!