I don't mind YAML. I dislike that something things become strings and sometimes they become other types:

   foo: bar   # {"foo":"bar"}
   foo: "bar" # {"foo":"bar"}
   foo: 42    # {"foo":42}
   foo: "42"  # {"foo":"42"} 

Other than that, no major complaints. My editor understands YAML and shows the indentation level in the background (highlight-indentation-mode) and auto-formats files so they all have consistent indentation (prettier-mode). As a result, it is not much of a nightmare to edit, despite the fact that semantic whitespace COULD cause you a lot of problems.