How could you best describe the passionate shepherd in the poem the passionate shepherd to his love?

Several peculiarities of imagination are present in this poem, although it is difficult to describe any of them as being metaphors or figures of speech. The pastoral imagery and tone allow the reader's imagination to "see" animals and workers, grass and hills, sunlight, shallow rivers and waterfalls, birds, and other less realistic things of beauty.

The poet mentions "melodious birds" singing madrigals to waterfalls. This is either metaphorical or a bit of personification, as madrigals can only be sung by humans. The intended effect seems to be the injection of pleasant sound into the pleasant imagery.

Later, the poet talks of making garments for his love out of flowers and greenery. This is fantastical, but it's not really metaphorical; neither is it using figures of speech. But it spins the imagination, to think of or envision such things.

It's also not likely that the narrator would have access, as a shepherd, to gold, amber, silver or ivory. Yet these valuable things are injected into the shepherd's promises to the one he wishes to take for his love.

So, what is the "desired effect"? The intended effect on his beloved is obviously to convince her to come and be with him. As for the intended effect on the reader, that is open to interpretation and personal opinion.

However, it does seem clear that the narrator wants the reader to share his feelings, and enjoy the pleasant imagery in his imagination. The narrator may also have wanted the reader to share in feelings of loneliness, or relative poverty made less poor by hope and imagination. He may have wanted the reader to share in the intensity of his longing, or to compare it to experiences of the reader's own.

The poem is a very interesting mix of reality and fantasy. As readers, we don't doubt that much of the imagery is very real. Even the birds singing "madrigals" helps us to hear the sound of them, and knowing they are singing to waterfalls, we hear those too, in our imaginations.

It might be pointed out that when he talks of "dressing" his love, it is much more fantastical than other parts of C. Marlowe's short poem. One could guess that if the poet is dressing her with only his imagination, he may be, in some way, complimenting her on what he envisions as being her nude form.

He is promising more than he can possibly deliver, but the point of this address to his beloved seems to be to emphasize the uncommon intensity of his feelings; and he hopes this will sway her.

In terms of metaphor and figures of speech, there really aren't any. But the exquisite fantasy, imagination and comparisons make this a very elegant poem.