Bought this after browsing through people's book lists on this site (a great place to find new books!) and finally started reading it yesterday. And finished reading it. It's a massive book so that should give an indication of how much I enjoyed it!
Reading other reviews here should have already given you an idea of the story's content, so I suggest you do what I did and just buy it. I tried not to let myself be too influenced by the reviews here, other than by being convinced that I would enjoy it - and I was right. I really, really enjoyed it and read it on the outward and return journeys on the train (3 hours each way).
The story is highly original and told from the points of view of Clare and Henry at different points in their lives. This is quite confusing at times but you soon get used to it. What's different and intricate is that you're reading the story out of synch, because Henry can exist in different times as he time travels through his own history. This in itself makes for an intriguing read.
But for me - the crux of the story is about love. Call me an old (young actually) romantic but I just loved this aspect of the story. Before you assume anything, I'm not your typical chick-lit reader - in fact I avoid it like the plague - but this is not typical chick-lit. It's so moving and beautifully told that I had to try not to cry on the train, and spent a long time thinking about it after I'd finished.
I know this review doesn't really say much about the plot but that's because I really think you should buy it and read it with an open mind. Prepare to be entertained - you'll laugh, wonder, and probably cry.