Apart from the theme of the modern existential crisis, what are some other dominant themes and motifs in T. S. Eliot's poem "The Lovesong of J. Alfred Prufrock?

Elliot presents his character, Prufock, also as being a pessimist contributing to his indicisiveness and inadequacy and that proper relations have eluded him.

i agree with mr. pedro  brites

In addition to the existential , metaphysical anguish of the modern man , Prufrock also typifies helplessness , uncertainty in a totally incomprehensible world. The arbitrariness and irrationality of a dream world inhabit prufrock's consciousness  leading him to chaos , disorder , monotony , emptiness and ennui where streets seem to be following with ' insidious intent ' and the evening fog takes on the hallucinatory image of a cat. The hollowness of the modern civilization is suggested when ' in the room women come and go / talking of Michael Angelo. These women are intellectual snobs having no idea about the power of his paintings.  Prufrock tries to ward off the horror of the inevitable ( I grow old I grow old ) by measuring out his life with a coffee spoon and in doing so he makes a caricature of himself. Both Guido da Montefeltro and Prufrock are in the same situation . The former is in the8th circle of hell and the latter is in a death -like situation where everything leads to inaction. Let us go then you and I ......and then nothing happens. The question is who is this 'you'.  

The futility, the emptiness of faith, sensorial experience of the death..