Kunitz tends to use plain, direct language yet somehow manages to pack in a variety of meanings. His poems feel grounded yet they also float around in a liminal, conceptual space. He mixes concrete images with abstractions, so even heady ideas are tethered down. Consider "The Layers" for example: one moment we're looking at camp-sites and the next a crazy-cloud voice is delivering a Zen koan.
Stylistically, Kunitz is a brave soul. He uses pure, succinct lines without shying away from complexity (or the occasional, emotional outburst). These pointed lines still have an organic movement, which probably stems from his deep connection with nature.
He loved writing, reading, and mentoring others until he was one hundred. Hints of that passion can be detected in "The Layers" from direct references to art and books, as well as the "lesson" portrayed by the end of the poem. Check out some other models of Kunitz's work, like "The Testing Tree" or "A Spark of Laurel".