I have recently found my favourite description of what narrative poetry means. Its in the introduction to 'A Book of Narrative Verse', compiled by V.H. Collins, with the introduction written by Edmund Blunden. I thought I would just share it's wisdom:

"A good narrative poem is a long strain of music accompanying a designed movement of human lives and passions, various in volume, in harmony, in time; its charm is not quite that of drama, with its stir and grasp and interrogation, nor of the novel, vigorous in direct action and multitudinous in characters and conversations. It is romance in closet relation to the ways of existence, and asking no strange, sudden transcendings of the imagination. The lyric and the ballad (so far as we may use these or any terms with a sense of limits) require of us an immediate syblimity."