Yes this a very good poem and it does include alliteration and 3 Onomatopoeias :D
To build motivation for the character gives a backbone to the story and about the Arthur for example if the Arthur got the motivation from seeing a kid take a candy out of a store that motivation for that character would be a bad guy or a heel and or antagonist there for the motivation for a character is very important they reveal it so you can get a bit of a background on the character in more information on the story and the Arthur.
I have written a similar essay. Except it was multiple pieces completed by two different artists. I would say start with the intro, then write the similarities in the second paragraph, the differences in the second paragraph, and the conclusion. If you need more paragraphs to reach requirements then do this:
1. Intro: give brief background to artwork and artist and write thesis
2. Similarities in technique
3. Differences in technique
4. Similarities in emotion conveyed
5. Differences in emotion conveyed
6. Conclusion: summarize comparison and rephrase thesis.
*no idea if this answers your question*
