Keats’s poem is similar to "Lord Randall" in terms of overall poetic style. The poem consciously imitates the form of a folk ballad, of which "Lord Randall" is a well-known example. Ballads were originally transmitted in oral form and normally exhibit a strongly repetitive and rhythmic pattern, like those of speech and song. These elements are present in Keats’s poem, where the first and last verse are almost identical, and also in "Lord Randall", which contains the refrain "For I'm sick at the heart, and I fain wad lie down," with some slight variation, all the way through.
Ballads usually tell a story, albeit a fairly simple one, and thus belong to the order of narrative poetry. This is true of both "La Belle Dame Sans Merci" and "Lord Randall." Both poems are also presented in the form of a dialogue, with the unhappy male protagonists, both of high social standing – the one a knight, the other a lord – being asked what has befallen them, thereby eliciting their tales of woe.
The style of the ballad is deceptively plain and simple, containing highly charged situations of love, death and very often, the supernatural, as in Keats’s poem; the beautiful but merciless lady of the title appears to be some kind of fairy who fatally entices the knight to her only to leave him drained and discarded on the bare hillside. The theme of fatal passion appears in both Keats’ poem and ‘Lord Randall’; Lord Randall, it appears, has been poisoned by his lady love, although in contrast to Keats’s poem there is no real suggestion that she is anything other than human.
The stark, spare style of both poems only serves to increase the overall impact. ‘La Belle Dame Sans Merci’ is, indeed, one of Keats’s most admired compositions, with its evocation of intense passion and its bleak aftermath:
And this is why I sojourn here,
Alone and palely loitering,
Though the sedge is wither’d from the lake,
And no birds sing. (45-48)
The major difference between Keats’ poem and "Lord Randall" is in the nature of their composition. "Lord Randall," being a genuine folk ballad, and therefore originally an oral poem, cannot be ascribed to any one author and has been rendered in varying written forms, although the essence of the poem always remains the same. However Keats’s poem is a literary work, originally composed in a fixed written form.
An assignment that I am working on wants me to assume that "La Belle..." is a rewrite of "Lord Randal." While I can see the similar themes, it seems like a stretch to assume that "L.R." informed "LBDsM" in any real way. What am I missing?