The fascinating part about this painting is the subject matter. Jesus washing the feet of his followers is the focal point, but there is something else. If you look closely, the other disciples in the picture are getting ready to be cleansed of their sins and are also helping each other out in the process. This really gives us a sense of feeling in the painting; the genuine gathering of friends in a way. Another aspect of this piece that really caught my eye was the long dinner-like table in the middle that is a great representation of linear perspective (the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight). This was the table that said to have been used during The Last Supper.
Tintoretto made good use of lighting in the composition. The appealing part about this is that the sky in the background is somewhat dark, which makes for the light shining in to be almost God-like. The contrasting of light and dark was done very well as Jesus is dressed very light in colours compared to Peter (as he is the opposite). This effect was mainly used during the High Renaissance (when Tintoretto painted it), and the technical term for it is called chiaroscuro. The religious circular lighting around everyone's head was pretty standard in most religious paintings done in The Renaissance.