The chief aspect of Romanticism that can be identified in this poem is the interaction between man and nature, and in particular the way that nature is presented as something that can impact the mood of man and bring joy and happiness. Note how this is captured in the penultimate stanza:
The waves beside them danced; but they
Out-did the sparkling waves in glee:
A poet could not but be gay,
In such a jocund company:
I gazed---and gazed---but little thought
What wealth the show to me had brought...
The daffoldils as they "dance" in the wind bring the speaker into a mood of unbridled happiness, and it is only later on that the speaker recognises that this sight is one that is of immense "wealth" to him because, as the final stanza states, he is able to remember it whenever he is feeling "pensive" and sad and the happiness he experienced when he first saw that sight is restored. What makes this poem such a powerful expression of Romanticism therefore is the way that it captures how nature can impact the mood of man and give him a reminder of the majesty of creation, which is enough to bring him out of his momentary troubles and remember that he is part of a universe that is much bigger than he, and his troubles, are.