What bothered me most about this adaptation was its handling of Maxim and the second Mrs. de Winter's relationship. Throughout most of the book, Maxim is reserved and standoffish toward the second Mrs. de Winter. Although he could be witty and playful, there was always a solid barrier between them. That's what made the scene where Maxim finally confesses what happened to Rebecca so potent. Finally, they (Maxim and the second Mrs de Winter) are able to be intimate because Maxim has let down his barrier.
In this movie, they are all over each other from the outset. There are a few moments of emotional distance between them, but the constant physical contact between them took away from the tension, loneliness and doubt that was so apparent in the book. And the ending - don't even get me started! That was so, so cheesy.