shall i compare thee to a summers day?

He's comparing his love to a summer's day and says that she's much more beautiful. All that follows discusses why she is far superior than even the most glorious season of the year. He talks about how she's physically more lovely and temperate (meaning she's of modest or even temper/personality). He then goes on to say that summer lasts for only a short time and then is gone, while her beauty lasts forever, and the sun can fade or wither the beauty of what it looks upon but her beauty never fades. All along those lines. The main metaphor is the love of his life compared to a summer's day. The mini metaphors and similes just pretty much break it down into specific ways that she's superior.