A fine question. "The Rime of the Ancient Mariner" exemplifies the Romantic period through the following:
1) It created exotic and imaginary alternatives to known society.
2) It emphasized the power of poetry (the Mariner telling the story).
3) It accented the power of the image (the albatross!)
4) It accented the importance of emotion, and of individual action.
5) It happened in a symbolic dreamscape, one full of meaning.
6) It incorporate Gothic/horror elements, another period development (see Frankenstein for example).
7) It uses relatively ordinary speech, a conscious choice on the part of the Romantic poets.