What is the outcome of revenge in both Hamlet and Frankenstein?

There are many themes in both Hamlet and Frankenstein, but revenge is a common theme in both texts. Why does revenge loom so large for the characters in these works? What is the outcome of revenge in both Hamlet and Frankenstein? Are the consequences of vengeance positive or negative? How might the authors, Shakespeare and Shelley, be calling into question the usefulness and ethics of revenge?