At first glance, not much. "The Passionate Shepherd to His Love" seems to be a pretty bland and unimaginative description of what goes on in the poem, particularly when you contrast the straightforwardness of the title to the poetic beauty of Marlowe's lyrics. But the contrast brings up an important point—Marlowe didn't name the poem. And while it's tempting to think that this makes the title less important, the Renaissance editor that slapped on the poem's conventional title has drastically influenced the way it is read.
The rather boring title names "the passionate shepherd" as the speaker of the poem. The mention of "shepherd" alerts readers from the get-go that this poem is going to be heavy on fluffy sheep, fields of flowers, babbling brooks, and other tropes of pastoral poetry. The title also firms up the addressee of the poem: the shepherd's love. So now the readers also know that country boy's got a crush and that he's hoping this poem will work some magic for his cause.
But these are all things that you can get from reading the poem—right?
We've been occasionally referring to the speaker as a he for clarity's sake, but if you look again, you'll notice there are no hims, hers, shes, hes, or any other gender-defining vocabulary words anywhere in the poem. The conventional title is actually the only thing that explicitly designates the poem's speaker as male (since he's not a shepherdess).
If this seems surprising to you, then Marlowe has done his job well. Writing gender ambiguity was considered a great skill in the Renaissance, and Marlowe's ability to write a poem that seems like it conforms to gender expectations without actually confirming them was thought to be pretty impressive stuff.
But hey, dude was a spy. So if anyone can pull it off, it's crafty Christopher.