To generalize your question a little, in my photography classes, I ask "What's the best photograph you've ever seen? And why?" Usually that promotes enough discussion that the principles of good imagery are well demonstrated.
I further generalize it to include motion imagery as well as stills, but specifically exclude edited motion media sequences from the discussion.
Or are you specifically focused on the final image? The print?
I'll leave the discussion of "Why teach chemical photography?" for others.