Lyric poetry is usually a short poem expressing personal thoughts and feelings. It is meditative. It is spoken by a single speaker about his feelings for a person, object, event or idea. When you read the poem, Frost is looking on back how he took the road that was less travelled by; while he is reminiscing, he remember how he feels and why he chose this road. A Narrative tells a story which has raising action, climax and a falling action. This poem does not have that.

I beleive the poem is lyric in nature. It tells the short story of Frost's life in 20 stanzas. He comes to the crossroads and decides to take the less traveled road, rationalizing that someday he will come back and conform, but knowing in truth he will not. He makes his decision and concludes that his decision to take the road less traveled has made all the difference. It expresses Frost's feeling about life and shows complexity of thought. Its cadence is lyrical.
An awesome poem by the way!!