It was surprising to find so many 1- and 2-star reviews here at Amazon. "Saturday" has a lot going for it. Much has been made of the technical impressiveness of McEwan's prose; his meticulous research into multiple topics; the attention to detail in the stream-of-conciousness narration of the central character, whose constantly calculating approach to life seemed entirely fitting for a brain surgeon (sorry, "neurosurgeon").
I found the meditations on the state of society and current affairs of 2003 particularly satisfying. One of the best sections was the argument between Daisy and Henry about the rationale for the Iraq war, youthful moral absolutism on the one hand and sloppy pragmatic consequentialism on the other. (My own position on this issue has oscillated between the two over the last six years.) There were some gripping moments (I won't spoil things by going into detail) and, perhaps, some clever allegorical points being made - invasive brain surgery being contrasted with invasive military action, for example. And I'm pretty sure that learning how Henry thinks has, in a small way, changed how I think, for the better.
On the other hand, it was equally surprising to find serious critics absolutely bowled over by this novel; words like "dazzling" and "stunning" seem to crop up a lot in reviews. They all seem to ignore the novel's most obvious flaw: a family of uniformly high achievers will not only be not particularly likeable, but, when the achievements are *this* impressive, almost certain not to exist. Yes, there's probably an 18-year-old kid somewhere who is currently being feted by the British Blues scene as our next greatest guitarist - but you can be sure that his sister isn't our next greatest poet, his dad one of our greatest surgeons, his mum one of our greatest media lawyers, his grandfather one of our greatest current poets and his poor grandmother "only" a "county champion" swimmer. How could McEwan go to such lengths with the details only to get the big picture so absurdly wrong? Some characters who actually act like human beings in a real family (occasionally stopping achieving things to make each other laugh, or drive each other up the wall, perhaps) would give the reader something to relate to. (One wonders if the reviewers would have been so gushing if they had been unaware of the identity of the author.)
There's lots more to be said but you probably have better things to do with your time. So in summary:
It's a brussels sprout of a book. You feel you ought to consume it, because you know it's good for you and you see everyone else doing it; and while you might not enjoy it much at the time, you'll feel slightly better for it afterwards.