Avengers: Age of Ultron (Joss Whedon, 2015)

or (the wholly expected tedium of escalating epicness) (spoiler notice)

This is the movie that broke Joss Whedon. It was so hard to make, with so much riding on it – not just the expectations of legions of fans, but the continued, steam-rolling success of the entire Marvel Cinematic Universe (MCU) – that after finishing, he couldn't even look at the film without seeing the flaws and compromises he had to make. He resigned his position as top creator at the studio. Sometimes, that's the toll of art. Looking at Avengers: Age of Ultron, you can't escape the feeling it was a sign of a monolith falling apart.