Within Shakespeare's sonnets, there are contradictions and complexities that certainly resist generalization on any topic or theme. Still, the portrayal of beauty and love prevail through most of the verses, sometimes in comparison, sometimes in contrast.
One example of contrast is that of Sonnets XVIII and CXXX. Sonnet XVIII, a Petrarchan sonnet, is an extended comparison of the young man's beauty to that of a phenomenon of nature:
Shall I compare thee to a summer's day?
Thou art more lovely and more temperate....
...thy eternal summer shall not fade
Nor lose possession of that fair thou owest;
In the Petrarchan manner, the beginning couplets present an argument that the final six lines answer. Unlike the season of summer which will pass, the lines of the poet will immortalize the beauty of the young man. Then, in Sonnet CXXX, Shakespeare creates an anti-Petrarchan comparison and flaunts the conventions of the sonnet sequence with its negativity. The "mistress," or young woman, defies every expectations of Petrarchan love poetry: rather than being elevated, she "treads on the ground."
And yet, by heaven, I think my love as rare
As any she belied with false compare.
Here Shakespeare presents no idealized love, no phenomenal beauty; yet, his love is a strong as any.
In Sonnets XXX and CXXVII, there is also a contrast, but this disparity exists with the tone of the sonnets regarding the beauty that they address. For, Sonnet XXX is a gentle sonnet albeit rather disturbing in summoning "remembrance of things past," and CXXVII is somewhat dangerous. When the poet thinks of his friend in Sonnet XXX, he is consoled for the past and its losses--
But if the while I think on thee, dear friend,
All losses are restor'd and sorrows end--
however, in the first of the "Dark Lady" sonnets, there is a sense of impending danger, lustful temptations, sinful desires. Beauty in the first is gentle and nostalgic, and its remembrance consoling; in the latter, there is danger and physicality in its dark, but beautiful temptations:
But now is black beauty's successive heir....
Sweet beauty hath no name, no holy hour
Comparatively, there is a new beauty found in each of these two sonnets as the poet finds beauty if memory, then in the dark temptations of passion in "eyes so suited."