To write a critical appreciation of the poem Journey of the Magi by T. S. Eliot, you need to move beyond pure summary and think about the underlying meaning and themes of the poem. A starting point is awareness that Eliot wrote this poem after he had joined the Church of England, and that it therefore is important to read the poem in light of how the journey of the wise men symbolizes the faith journeys of both the reader and the poet himself. Thus the difficulties of the winter journey are emblems of the obstacles to a faithful Christian life.
The main theme you might consider is that of the meaning of birth and death in religious context. Here Eliot seems to make the idea of the approaching death of the magus (an old man in the "now" of the poem), and the death of his Zoroasterian faith, a matter informing how Christians should think of their own ultimate journeys from birth to death:
… were we lead all that way for
Birth or Death? There was a Birth, certainly,
We had evidence and no doubt. I have seen birth and death,
But had thought they were different …