It seems there are 2 sides: one side that thinks the movie is a disappointment, the other side thinks it is marvelous with an excellent performance.
I think the movie may disappoint some who expect more action than drama but it shouldn't affect the quality of the movie. Personally, being a mid-aged person who loves psychology, sociology, political criticism and literature I found this movie a masterpiece. It makes you feel like you have read a classical novel and very satisfied. In addition, the soundtracks were marvelous that makes you feel the thrill and the darkness inside a sick man.
Moreover, the act of Joaquin Phoneix was exceptional and deserves an Oscar, period!
I highly recommend it to ones who love realistic drama rather than merely an action movie.