This poem reflects the characteristics of the Romantic period in that it does reflect a love of and respect for nature, it uses supernatural elements of a fantastic nature, and elevates the common man (a sailor) as its hero. It does not reflect romantic characteristics in its use of archaic language (eftsoons he droped his hand, etc.)
The end of the poem really reiterates the romantic concept of the connection between man and nature: "He prayeth well who loveth well both man and bird and beast." Also, the entire poem is a "nightmare vision" which reflects the romantic interest in the supernatural. The romantic fascination with nature is also played out when the Ancient Mariner has to tell his tale for penance because he violated the covenant between man and nature. Finally, the remote setting of the poem reflects the romantic interest with the "hermit" archetype.
Here are some more specific examples of the romantic influences in the poem:1) The power of nature – The major symbol that develops the power and the beauty of nature is that of the slimy creatures from part 4 in the poem. At this point in the poem, the mariner is surrounded by 200 corpses (that of his crew). He feels guilty for having led them to their demise and he wishes he could join them. He looks down from his boat and is able to see the beauty in even these ugly, slimy creatures. Realizing that they are made by God, he is able to pray for the first time in a long time. Here, as in most romantic literature, nature has the power to heal. The mariner is now in God’s favor.2) Sin and repentance – One of the major themes from The Rime of the Ancient Mariner is that of sin and repentance. The mariner shot the albatross for no apparent reason. Because of this lack of respect toward nature, the mariner lost God’s favor and is unable to pray. As a punishment, his crew members tied the albatross around the mariner’s neck as a punishment for their bad luck. However, when the mariner is able to see the beauty in the slimy creatures in the waters below, he realizes that these creatures are beautiful in God’s eyes and that he should have seen the beauty in the albatross. At this very moment, the bird falls from his neck and falls into the water – proof that he has been forgiven.
4 characteristics are the evidence of nature, self-reflection, atonement and repentence, and salvation. There are also more characteristics of the Romantic Era in it, as well, which I'm sure others may provide for you.