The physical structure of the poem is also interesting with these two poems. Naturally, as Raleigh's nymph is turning Marlowe's shepherd's letter of its ear, the same structure is used for the second poem, along with the same metaphors. The imperfect rhyming is also consistent between the two poems. It is unclear what the purpose of the imperfect rhyming ("love" and "move") might be, unless pronunciations were different when these poems were written. If the pronunciations where not different, they could perhaps indicate that the shepherd is not the most literate, and is guided more by passion than by impeccable verse.

The response is effective in part because it contradicts the heavily romantic imagery that the shepherd is using -- madrigals, beds of roses, fragrant flowers. That these are directly argued against in the nymph's reply ("flowers do fade," for example) makes the point that no matter how glorious romance might be at first, the glory of it will wane and cold reality will set in.

The fact that the second poem is a direct reply to the first is interesting. Raleigh could have made the same points independent of Marlowe's work, and so it is interesting that he felt his points could be made more effectively by contrasting them directly with an example of unbridled romantic...

In doing this, Raleigh imbues his own poem with the context that strengthens the argument. Without this context, Raleigh's poem might read as universally bitter. Such a poem would be less effective, because the reader would have no context from which to view the narration, but with the context of young love, Raleigh's bitterness has more meaning.
Overall, this pair of poems is effective not just for the messages each conveys, but for the pairing of the poems. The two messages put together complement one another -- the second does not entirely invalidate the first, it simply provides the rest of the picture. As such, the poem captures, in the way that there is a spring and a fall, the blossoming and fading of love. The two works combined, therefore, mean more than either individually. They represent a more complete expression of the human condition. This message follows the nature metaphor clearly. The only issue I take with these two as a pairing is that Marlowe had no opportunity to respond to Raleigh's message. I take away from the debate between the two poets/narrators that just because we have fall and winter does not mean we shouldn't enjoy spring and summer while they last. That message, had the shepherd been given a chance to address the nymph again, is likely what he would have conveyed.