Oh, lord, are you sure you want to get me started on that one?
Ahem... first off, what sort of a project are we talking about here? Is this for school? Are you writing this with hope of publication in a journal? etc. Donald R. Burleson wrote a quite nice piece on "Nemesis" some years ago, if you can find it. And I've done a brief, sketchy bit on it myself, which I'm planning on expanding later on. (De Camp's comment to the contrary notwithstanding, it really is a rather evocative and eerie piece of verse.)
So... are you looking for just a description, or would citations of secondary sources help as well?
For the moment, how about going straight to the horse's mouth?
Another recent production of mine, which I will enclose [in a letter to his friend Rheinhart Kleiner of 8 Nov. 1917], has a very different metre & appeal. I think I shall send this piece -- Nemesis -- to The Vagrant, since [W. Paul] Cook seems fond of the unusual. It was written in the sinister small hours of the black morning after Hallowe'en, which may account for the colouring & atmosphere! It presents the conception, tenable to the orthodox mind, that nightmares are the punishment meted out to the soul for sins committed in previous incarnations -- perhaps millions of years ago! The hybrid metre, a cross betwixt that of Poe's Ulalume & Swinburne's Hertha, ought to satisfy the couplet-hating souls of yourself & [Maurice Winter] Mo[e].
-- from Selected Letters I: 1911-1924, pp. 51-59
If you'd like to discuss this one further, let me know....
EDIT: And, if you haven't guessed -- I'm delighted to see someone taking the Old Gent's poetry into account, since he considered himself a poet during the early years, and even later on (especially 1929-30) he wrote some fine poetry. Most of his poems are anywhere from mediocre to bad (
as poetry, though there's always a lot to be gained from them otherwise on varying levels; this is where his intense love of the 18th-century versifiers tripped him up most often), but when he did hit it right, he really hit it right!
And how can you beat that opening (and closing) stanza:
"Through the ghoul-guarded gateways of slumber,
Past the wan-mooned abysses of night,
I have lived o'er my lives without number,
I have sounded all things with my sight;
And I struggle and shriek ere the daybreak, being driven to madness with fright."