In the New York Times last year, there were 690 movie reviews. That's almost two films a day. While no one reviewer saw and wrote about all of those films, the number alone tells you that there were a lot of films out there.
After a while, movie reviewers can have a hard time separating films. To make your film stand out, it has to be different in certain ways.
Critics often like period pieces, especially slow-moving period pieces. There aren't that many of them, so they tend to get points just for trying.
Critics have seen a lot of things that you and I haven't, just because they see so many films each year. What seems new to us may be old hat to critics. Beyond that, there is the fact that most critics look for different things (camera angles and the such) that you and I don't notice so much. Critics are often trained to notice what doesn't stand out so much for the general public. Critics see movies differently than you and I do, and people who make movies for a living also see things that we generally miss.
As for the casting, this relationship is supposed to be too shallow to survive the problems coming at them. Yes, it would be nice to have the big romantic scenes be hotter, but if they were, you'd wonder what happened to this couple.
If it makes you feel better, several reviews by the general public at movietickets.com and rottentomatoes.com are mixed, with several saying that the movie was boring. And I can certainly understand it. This is far from an action picture, and certainly isn't a comedy. And as a romance, it's different.