"Watch Rooney Mara do stuff" is a good enough pitch to get me to watch your film.
If you don't like this movie, I know exactly why. It's not for everyone, but I believe the best movies have niche audiences. I personally found this film ethereal and contemplative in all the right ways. The cinematography and score are the two biggest standouts here (alongside Mara's acting, but I could gush about her all day). My favorite scene from this movie is easily what you can find on youtube by looking up "a ghost story music scene", where Affleck's character plays his girlfriend a song he made. It's just really good. Go watch it.
And watch the movie too. You might not like it, but you might love it. It's just that kind of film.