I'm still processing this. The comparisons to "Taxi Driver" are fair: the performances, the director's vision and exectution, the understated script..... those are some of the similarities. The major differences, for me include the depth to which the protagonist's trauma is not played out for us to view as observers, but drip-fed in increasing doses, often from a first-person perspective, which in my watching felt more like we were experiencing Joe's trauma with him, rather than seeing it played out for us. The film also has a lot of relevance to current discussions of modern masculinity, and here the gendering of social roles is presented very much more as a question than a statement.
If you prefer to finish watching a film with your friends and be able to agree pretty much without discussion on what it was about, then I suspect you might find this film pretentious or light on plot. If you're the type who enjoys discovering what your friends think they just saw, and don't mind spending a lot the movie time watching Joaquin Phoenix' face doing some really admirable acting, then this film might be as worthwhile for you as it was for me.
If you prefer to finish watching a film with your friends and be able to agree pretty much without discussion on what it was about, then I suspect you might find this film pretentious or light on plot. If you're the type who enjoys discovering what your friends think they just saw, and don't mind spending a lot the movie time watching Joaquin Phoenix' face doing some really admirable acting, then this film might be as worthwhile for you as it was for me.