One of the most obvious differences between the tragic figures of Macbeth in Shakespeare's Macbeth, and Victor Frankenstein in Mary Shelley's Frankenstein is the motivation of each man. Each is ambitious, but whereas Macbeth simply wants power, Victor believes that he might be able to serve mankind if he can conquer death by creating life.
Macbeth has no reason to kill Duncan other than to become more powerful: he is not a rebel against a tyrannical leader, as Macduff becomes when Macbeth has murdered not only King but countless subjects—including Macduff's entire family. Macbeth realizes that his reasons for killing Duncan are self-serving: he will become King of Scotland, and his wife wants to be queen, but Scotland will not benefit. Even while he has doubts, his wife berates him until he agrees to kill Duncan, noting that ambition is all that drives him.
I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself,
And falls on th'other... (I.vii.25-28)
On the other hand, Victor Frankenstein is ambitious, but he believes that if he can control life, he can cheat death, thus serving mankind. He diligently searches to find the secret of creating life:
I thought, that if I could bestow animation upon lifeless matter, I might in process of time (although I now found it impossible) renew life where death had apparently devoted the body to corruption.
Unlike Macbeth, Victor's motivation can be found in his desire to allow people to live longer by controlling death. However, at the same time, his is misguided and acts like God.
Macbeth has no desire to help anyone but himself. Victor wants to help mankind. But both men respond to a desire to be greater by the actions they take. Macbeth is selfish; Victor wants to help, but also wants to be recognized for greatness:
A new species would bless me as its creator and source...
Victor lacks a sense of responsibility and humility, necessary to truly help others more than benefiting himself (specifically, his ego).
Both men suffer enormous loss because they overstep—Macbeth, the boundaries of society, and Victor, those of science.