Clarity, consistency of form, and in a word – perfection!
There’s a reason Shakespeare is Shakespeare, if you get our meaning. You don’t become the most famous and widely beloved poet of the English language by writing shoddy, confusing verse. Working within the strict, somewhat stiff constraints of the sonnet form, he produced poems that are simultaneously high-flown and down to earth; while they do employ what we all think of as "Shakespearean" language – you know, the whole "Doth thou thinkest me not a wondrous poet?" kind of thing – the sonnets are notable for their frankness and clarity. This one in particular is recognizable for its very simple language (for Shakespeare’s time, that is), elegant structure, and logical flow.