If it does not have abundantly described nature in it, it is not a Romantic poem. In The Chambered Nautilus, written by Oliver Holmes, the mollusk in question has all the favorable features it possesses described in boundless extent, as well as the beach its abandoned shell was cast upon (1-7). The shell is described as a ship of mother-of-pearl, on something of an enchanted beach, complete with sirens and mermaids. Longfellow's poem written after the death of Nathanial Hawthorne takes time to describe the weather, the setting, and the people around when he found out his friend had died (which really seems a little superfluous) (1-14).
Another Romantic poetry theme is that of strange and far away places. The exotic is dear to a poet's heart. In Holmes' poem, the shell is found on that wondrous shore with mythical maidens abound. In another of Longfellow's poems, he describes the coming of autumn like that of an ancient king in all of his splendor (5-6). Both of these are really quite exotic because how often do you see mermaids or long dead kings? They take so much care to put these things in that I have not read a single Romantic poem without a mention of something similarly strange and weirdly exotic.
Another similarity between Holmes and Longfellow is that neither seem to care much for religion. In The Chambered Nautilus, Holmes writes that the sea creature should grow to be free even of heaven (33-34). Longfellow's poem of mourning is surprisingly void of any mention of an afterlife, which is normally a comforting thought to those who have lost someone they love. I think that via this omission it is reasonable to infer that Longfellow thought little of religion. While lack of religion is not really a standard of Romantic writing, I have noticed that it does occur quite a bit.
The big difference between Holmes and Longfellow is their choice of themes. When Holmes was writing The Chambered Nautilus, he was trying to express his thoughts on how important it is for a person to continue growing through out their lives. Both of Longfellow's poems were about his feelings and perceptions, instead of more serious themes. In addition to that, they used different meters and rhyme schemes, but that really is not much worth mentioning.
Holmes, Oliver. "801. The Chambered Nautilus. Oliver Wendell Holmes.
1909-14. English Poetry III: From Tennyson to Whitman. The Harvard Classics."
Bartleby.com: Great Books Online -- Quotes, Poems, Novels, Classics and Hundreds
More. Web. 07 Dec. 2011.
Longfellow, Henry. "Sonnets. Autumn. The Belfry of Bruges and Other Poems. Henry Wadsworth Longfellow. 1893. Complete Poetical Works." Bartleby.com: Great Books Online -- Quotes, Poems, Novels, Classics and Hundreds More. Web. 09 Dec. 2011.
Longfellow, Henry. "Hawthorne. Flower-de-Luce. Henry Wadsworth Longfellow. 1893. Complete Poetical Works." Bartleby.com: Great Books Online -- Quotes, Poems, Novels, Classics and Hundreds More. Web. 09 Dec. 2011. http://www.bartleby.com/356/224.html.