I've never been a huge Johnny Cash fan (in fact, I always preferred Waylon Jennings in the bad boy of country stakes. :P), but never the less, I quite enjoy this sort of biopics.
All in all, the movie was quite predictable (in terms of how biopics are played out) and in some ways a very cliché story of fame, drugs and passion. Joaquin Phoenix most certainly gives his all and wears the Johnny Cash suit with relative ease, seeing how hard it is to portray someone known for being 'unlike anyone else'. The problem I have with Phoenix at times is the fact that he throws himself so completely into his roles that sometimes you start feeling a little detached from the character, you just look at him acting hard. And there were moments where I felt like this. Don't get me wrong though, I don't think there's anyone who could have done a better job.
As shocked as I was to see Reese Witherspoon pick up the Oscar for playing June Carter, I was happy to learn that it was for good reason. She kept the movie grounded and was so genuine in portraying what her character was feeling that I think she gave a heart to the movie. The best thing about the whole film was the chemistry between the main actors and the way the Cash/Carter love story was played out - in anything but sentimental way. It certainly tasted like life. I don't think the film was larger than life, but perhaps that also helped in making it feel more real.