First, let's understand what a lyric poem is. Historically, a lyric poem was intended to be sung, so rhyme and rhythm are important to the structure of a lyric poem. Lyric poems in modern times may not be set to music but still are very expressive of the poet's emotions.
According to this definition, The Raven is an excellent example of lyric poetry, although it may be a little long compared to the usual lyric poem. The choice of words and use of strategic pauses creates an unvarying meter throughout the poem; eight pairs of stressed and unstressed syllables in every line. The only exceptions to this pattern are in second, fourth and fifth line of each stanza, where an extra unstressed syllable is not included. In the sixth line of each stanza, there are three pairs of stressed and unstressed syllables and an extra stressed syllable at the end.
The rhyme scheme of the poem is also constant and unvarying, which lends to musical feeling of the words and contributes to the overall impression created.