Summer is presented in a traditional way ... but in unusual images and language. Summer is traditionally presented with winds and buds and sun and fair beauty of foliage. It is Shakespeare who takes the traditional and creates unusual images with unusual language to subtly divert the presentation away from the traditional. His winds are "rough" and "shake the darling buds of May," ruffling them and even dislodging them. His summer's days have a "lease" that is "too short a date." His sun is the "too hot eye of heaven" that can have "his gold complexion dimm'd" instead of shinning merrily all the time. His "fair" summer images "from fair sometime declines" because of "nature's changing course untrimmed." His traditional presentation of summer winds up as a contrast as he shows that all beauty fades--except that which he makes immortal in his sonnet.
Poetry is always a fresh, unique way of perceiving what is within and around us. Of course, Summer is presented in a nontraditional way by Shakespeare, one of the greatest writers of all time. It is this unusual way that strikes the reader, thus preserving the beauty of the verse.
The final point of the poem, found in the final two lines (couplet) is that while people and seasons and weather are changeable and ending, the lines of this poem are permanent and lasting, as are the ideas he is expressing in it. He says in line nine that "thy eternal summer shall not fade." And he was right; here we are 400 years later talking about how the subject of the poem is more lovely than a summer day. The person is dead and gone, but not the idea of him or her.
I think that the use of summer becomes more effective when it is compared to the context of the person with whom there is a shared love. The concept of comparing loved ones to weather is not really new, but the way it is presented in this sonnet is unique. Weather is unpredictable, changing and features moments of discomfort. The love the speaker shares with the other person, though, is constant, filled with moments of comfort and security. This is a new way to see the link between weather and love.
The idea that summer is brief is not exactly revolutionaryl, but within the context of the poem, summer is presented in a bit of an unusual way. Instead of being celebrated for its glory and loveliness, its flaws are expressed. There are "darling buds" in May, but the winds of May are "rough." The summer sun is sometimes too hot, and it is often obscured by clouds. By presenting summer as less than ideal, Shakespeare is extolling by contrast the superiority of the subject of his poem.