Lets be clear, the vast majority of fans enjoyed or greatly enjoyed Avengers: Age of Ultron. The film is well on its way to crossing the billion dollar mark at the internatinola box office and Marvel is looking strong entering Phase 3. Still, there were a small contingent of comic book fans and super-feminists unhappy with the film and Joss' portrayal of Scarlett Johansson's Black Widow (the latter need to remember that Joss had to alter his plans for Scarlett due to her pregnancy).
While the greater percentage of moviegoers definitely enjoyed the film, at the end of the day, the smaller/unsatisfied contigent is still a number that's nothing to sneeze at. As evidenced in just a few of the tweets above, the vitrioll was thick.
Coming to Whedon's aid is Guardians of the Galaxy director James Gunn.
Indeed. However, as with most things in life, it's that 5% that ruins things for the rest of us.