I have just seen it - and it was pretty good.
It doesn't actually seem too dissimilar to the book - although obviously sub-plots are left out. (The book makes much more of the car crash, and also Henry's father's landlady and his childhood. In the book, Gomez has a huge crush on Claire, which is only hinted at, and there's also the rather tragic story of Henry's previous girlfriend - as evidenced in the film only by the lipstick found in Henry's bathroom cabinet)
I am a bit upset about the omission of one of later scenes in the book (possibly even the last), and one of the saddest, in which Henry travels forward and visits Claire in her dotage (possibly on her deathbed). I recall it moved me to tears, the only bit of the book to actually do so, so was surprised to find it had been removed from the film...