While these two poems are related (specifically, one is the "answer" to the other) and share many things, they are fundamentally two different types of poetry. Let us first look at the superficial differences and similarities, and move to the deeper ones.
The meter (that is, the number of syllables and beats per line, and the placement of the stressed syllables) is very similar -- although not exactly so -- in these two poems. Specifically Ralegh (his name, like Marlowe's, can be spelled several different ways -- Elizabethan spelling is not an exact science!) is copying, with slight changes, Marlowe's "Come (or to or then) live with me and be my love" line (lines 1, 20, and 24 of Marlowe, lines 4, 20, and 24 of Ralegh) for which Marlowe's poem became famous, so the meter would have to match in order to fit this line into a poem with any sort of regularity. The meter of both poems is a very regular iambic tetrameter (4 beats to the line), with the vast majority of the lines containing exactly 8 syllables (each poem varies only 5 lines out of 24.) The rhyme scheme for both is aabbcc, etc, with first stanza rhymes (aa in Marlowe's case, bb in Ralegh's) repeating in later stanzas. These are doubtless very similar poems, and each with a pastoral (meaning an imaginary world of rural lovers) setting and speaker.
But beyond these similarities of poetic form and subject, what is different about these poems? The answer is tone. Marlowe's poem, written first, is (as far as can be determined) an entirely sincere poem written in the very old and hallowed pastoral style of the entirely imaginary educated Shepherd wooing his beloved (a nymph, or perhaps a maiden) with gifts and promises of an enchanted rural life. This is poetic form rather than a reflection of reality, for very few real shepherds in Marlowe's day could have provided "coral clasps and amber studs", or any other of the gifts described. Marlowe's poem, written in an old and codified form, nevertheless expresses a real emotion. You could compare it to rap music, in which certain slang words and tropes are used that are familiar and repeated in other songs, but can still express a true emotion of the singer.
By contrast, Ralegh's poem is a satire of Marlowe's. Ralegh takes Marlowe's sincere poem, and turns it into a realistic rebuttal of the silliness of pastoral love poetry's promises and images (and it is perhaps a satire on the very idea of codified forms of poetry itself -- both ideas would probably have amused Marlowe just as much as Ralegh). Ralegh takes all of Marlowe's images and, in the voice of the previously silent "nymph" explodes the myth of pastoral love. It begins "If all the world and love were young" (Ralegh line 1) -- which the world and love certainly are not -- and she commences to show how all of the Shepherd's promises are either impossible or impractical. For this, one has to assume that Marlowe thought of his original Shepherd as a real person, and not a poetic expression (which he almost certainly did not) -- it is a bit like addressing political questions to a Sesame Street character. It is inherently funny, and Ralegh continues this theme, and even gets a little dark at the end of the poem. Not only, Ralegh says, are formal poetry and buccolic love impossible, but "Had joys no date nor age no heed", bringing up the spectre of death.