Some folks dislike cinnamon. They claim it is bitter - and I can agree with them.
I've never figured out whether there is any "true cinnamon" available in our soopermarkets. Anyway, I probably wouldn't be able to tell the difference from what some call cassia, not cinnamon.
Cinnamon is somewhat bitter but, for the most part, I like it. And, altho' I could really take or leave zucchini prepared other ways, I like zucchini bread .
Steve oh and if you like walnuts in your bread, as i do, they become bitter with age.