Hey there!
This aspect is the fact that he used blank verse instead of a traditional rhyming meter.
Other poets used rhyming meters. They kept the poem with rhythm and the words weren't jumbled and nonsensical. It kept it like a story, but still a poem, and had a fun and understandable way of being read with a consistent tempo and speed.
Robert Frost, on the other hand, created his own new style of poetry that he was looked up to for doing so, because he broke nearly all the current rules of poetry, and used no rhyming meter. He used the verse he thought would suit his poems best- and indeed they did.
Hope this helps!