Would "Shall I compare thee to a summer's day?" be a Metaphor?

This Isn't a metaphor

Explanation:

Metaphors are used not to compare but to add exaggeration.

Even though there isn't "like" or "as" in the text he still uses the word compare in a context where you can infer he knows she is indeed not the summer's day, but could be describe as such.

Metaphor ex: My face became a tomato as my classmates laughed at me.

Slimily ex:  My face was as bright as a tomato after hearing the mocking laughter of my class. I could be more embarrass, I internalized with my eyes stuck to the floor.

Similes compared to things. Metaphors do not.

c.to compare several aspects of the tragedy to other worldwide tragedies