There are some general similarities between these two sonnets, though there are more, and more substantial, differences between them. Poetic analysis covers every particular of poetry from structure to literary techniques and all that lies between. Because of the limited format eNotes offers, it will not be possible to give more than a general comparison of general analyses.
The first difference is in structure. Petrarch, who originally developed the sonnet form, structured this sonnet as one octet (8 line stanza) followed by one sestet (6 line stanza. Petrarchan form requires 14 lines in sonnets. Shakespeare, who learned the sonnet form from the adaptations to Petrarch's form innovated by Wyatt and Surrey, structured this sonnet as three quatrains and one couplet (couplets always have end-rhymes). Rhyme schemes for each form also differ: Petrarch, abbaabba cdedce, with a concatenated (linked) aa couplet at lines 4 and 5 resulting in a total of three couplets; Shakespeare, abab cdcd efef gg, with only one end couplet.
One similarity is that both sonnets speak of love that has lost the luster of beauty, in fact, Shakespeare speaks of love that seemingly never had the luster of beauty. One difference is in how the poets speak of this presently lusterless love. Petrarch speaks with saddened love and fond remembrance saying that though the bow is Cupid's arrow is no longer "bent" by his beloved, the "wound" of Cupid's first arrows still is active: he still loves her as though she were what she once was.
She did not walk in any mortal way,
But with angelic progress; when she spoke,
Unearthly voices sang in unison.
Shakespeare speaks of his lusterless love with biting irony calling froth images of beauty that she is or has not and comparing her to what she is not. His paradox in the resolving couplet states his adamant acceptance and admiration of her notwithstanding missing luster.
And in some perfumes is there more delight
Than in the breath that from my mistress reeks.
And yet, by heaven, I think my love as rare
As any she belied with false compare.