What criticism does Hamlet have for his mother?

I think you mean in Hamlet's soliloquy in act one. Hamlet considers his mother to be weak and to lack grief for his father. Hamlet accuses Gertrude of hanging off the arm of Claudius like a schoolgirl in love. Hamlet paints all women as fickle and frail because of his mother.

Why, she would hang on him
As if increase of appetite had grown
By what it fed on; and yet, within a month-
Let me not think on't! Frailty, thy name is woman!-