One of the overwhelming aspects of the poetry of Keats is his capacity to describe his scenes and senses by appealing to a variety of the senses. One of the techniques he uses to build up this sensuous description is synesthesia, which is where one sense experience is described as another. Consider how in "Ode to a Nightingale" the speaker comments that he "cannot see... what soft incense hangs upon the boughs." The sense of scent is hear described as the sense of sight, which helps build up his incredible sensuous description.
Keats uses a lot of imagery in his odes. He describes things in great detail. It helps us feel like we are there. We can picture it in our heads. A great poet chooses just the right word to evoke the sense he wants, and uses that sensuousness to create meaning.