Poetic language ought to have zing, oomph, or pizzaz. The exact word you want would depend on your preference. Dynamism, energy, a charge.
The only exception is a deliberately understated or neutral language. This language would have to be absolutely blank, and its charge could consist in the deliberate repression or withholding of any kind of color or spice. It would have to be exaggeratedly neutral, if such a thing is possible. An extreme asceticism. This might be a limitation on my part, but I cannot view William Stafford & the like as poets. The language has to do something.