How does the poet create atmosphere using suspense and drama?

The mere opening of the poem creates a sense of suspenseful drama as the speaker comes across a home with no one there.  The opening words of "Is anybody there?" implies a great deal.  The reader is left to ask if the speaker is new there or has the speaker been there before.  Is this a visit or a return?  The details add to this atmosphere of intrigue.  The "moonlit door", the forest's silence, the "ferny floor" underneath the horse's hooves, as well as the bird flying out of the turret help to establish a mood that underlies drama or suspense.  The lack of response and the description of the traveler as "lonely" helps add to this, implying that while the speaker is without anyone else, something else is there.  The speaker is not alone.  Punctuating the growing silence would be the closing words of "Tell them I came" and "I kept my word."  These lines add to the drama of the moment. The reader is left to ask what was the promise the speaker fulfilled and who is "they"- the individuals that were supposed to be there waiting for him?  As the speaker and horse leave, such questions plague the reader, and contribute significantly to the suspense and drama atmosphere of the poem.