What do you make of Shakespeares reference in the final two lines that his love is rare and belies that of false compare?

Is speaker in [My mistress eyes are nothing like the sun] ultimately as critical of his mistress as remarks such as black wires grow on her head (line 4) suggest? What sense, if any, does the poem give you of what she looks like? If Shakespeare isnt criticizing her, then what is he saying about her by describing her features in this way? What do you make of his reference in the final two lines that his love is rare and belies that of false compare? As with all Discussion Posts, to get full credit, your responses must be at least ten sentences.