I'm a huge fan of Batman and believe it or not, a huge fan of Joker.
I didn't have any expectations of this movie and I deliberately stopped watching trailers as I didn't want to form an opinion before I saw it.
I can honestly say I was impressed, as a fan and as a movie watcher it was great. A friend of mine who isn't a fan watched it with me the second time and also immensely enjoyed the movie.
As bonus credit, all the little homages to other movies and not just DC inspired movies were great for the feel of the movie. I'm not sure why some critics don't like the movie, maybe they expected something different.
Pheonix deserves an Oscar nomination for this.