I just watched an animated feature that had to be an absolute nightmare to direct.
It allowed no comic relief, nor amusing animal sidekicks, nor even squash and stretch. Every line of dialog had to be said with either deep reverence or snarling cynicism.
And on top of that the main characters could never be shown on screen or even heard speaking. It was rather like watching a movie about the Invisible Man... if the Invisible Man had stayed in his trailer for the entire shooting schedule.