Thematically both poems are similar. Both place an emphasis on nature and its importance. Both poems are also mainly about the speaker making a choice. The choice for both speakers is the same as well. In both poems the choice is made to follow their own beliefs and not follow what the world is telling them or showing them. Frost chooses to take the road less traveled. Oliver chooses to listen to her own voice and save the only life she knows that she can save . . . hers.
In contrasting their themes, Frost's poem emphasizes a much more internal struggle and decision-making process than Oliver's poem. Frost is on a road, by himself, and the only outside influence is which road looks more worn. In Oliver's poem, however, there are other people's voices actively trying to sway and influence her internal thought processes. She has to move away from all of that to hear and feel clearly. Frost is already alone.
Structurally Frost's poem has 4 stanzas each with 5 lines. The rhyme scheme is ABAAB. The rhythm is a bit tougher. Some might say it is iambic with an unstressed-stressed beat pattern to it, but that doesn't fit quite right since each line has 9 syllables. An anapest works for that, but the stress doesn't always land on a syllable or word that is typically stressed. For example in the opening line, an anapest would put a stress on "a."
Oliver's poem is written in a single stanza of free verse, so there is no rhyme scheme or set rhythmic meter. There are some internal rhymes here and there, like the "knew/do" in the opening two lines.