How did it compare to the book?

Not at all. Other than the title and the same basic premise, it was a completely different story.

This was a light-hearted romantic comedy, while the book clearly isn't.

I was only partially paying attention to the movie, but they completely ditched the characters' histories from the book. No mention of Elise's daughter and her tragic death. No mention of Nicholas driving drunk as a teenager and killing the mother, father and child who were out for a walk.

And unless I missed it, Nicholas hadn't met Elise before, as he had done in the book.

Also, in the book Nick is already a partner, so that wasn't the reason for the contract.