In Shakespeare's Hamlet, Hamlet is heart-broken over his mother's "o'erhasty marriage" (II.ii.60), but he is appalled and enraged by his father's murder.
Hamlet cannot understand why his mother has married someone so different than his father. At the start of the play, Hamlet is disgusted by his mother's remarriage to Claudius. When Horatio mentions that he came for Hamlet's father's funeral, Hamlet sarcastically notes that Horatio probably came for his mother' wedding—the wedding which followed so quickly after the funeral. Hamlet darkly points out that they might have used the funeral food for the wedding feast in that his mother married so fast on the heels of Old Hamlet's death.
Thrift, thrift, Horatio. The funeral baked meats
Did coldly furnish forth the marriage tables. (I.ii.185-186)
When Hamlet confronts his mother about what he also believes is an incestuous marriage (marrying her husband's brother), he wonders how she could go from such a noble man only to marry his brother who is, by comparison, like a piece of rotted flesh. He directs Gertrude's attention to Old Hamlet's picture:
Look here upon this picture...
See what a grace was seated on this brow... (III.iv.59, 61)
Then Hamlet directs his mother's attention to the portrait of Claudius, asking (in essence) if she is blind:
Here is your husband, like a mildew'd ear
Blasting his wholesome brother. Have you eyes? (70-71)
This is not as horrific to him as the murder of his father. His mother may appear (to him) to have been unfaithful to her husband's memory, but she did not take his life, nor was she involved in his murder. His father's death by his own kin, and the Ghost's deep regret of meeting his Maker with a soul laded down with unrepented sins, make Claudius' actions a crime, whereas his Gertrude's actions were not.
We know that the condition of Old Hamlet's soul at his death is something Hamlet cannot overlook when he has the chance to kill the King and refrains because he does not want Claudius' soul to go straight to heaven, as his father's soul could not:
...now he is praying;
And now I'll do't. And so he goes to heaven,
And so am I revenged...
A villain kills my father; and for that,
I, his sole son, do this same villain send
To heaven. (III.iii.76-80)
Hamlet expects the worst he could do on behalf of his father would be to kill his murderer and send that murderer to his reward, rather than to his punishment.
Hamlet does not wish to kill his mother for what she has done. He takes the Ghost's advice to leave her alone.
But when Hamlet kills Claudius, there is no way to measure his fury over his father's death, his mother's remarriage, and Claudius' duplicity—which also costs the lives of Gertrude, Laertes and Hamlet. Laertes confesses his part in the crime, but reveals the King's guilt:
…The King, the King's to blame. (V.ii.328)
Hamlet, then, takes his revenge:
Here, thou incestuous, murderous, damned Dane,
Drink off this potion! Is thy union here?
Follow my mother. (332-334)
The murder of Hamlet's father causes Hamlet more confusion and sorrow than his Gertrude's remarriage.