Tricky - very tricky.
I actually felt really sorry for Frankensteins creation. Shunned by his creator, abandoned like a child - unable to remember his previous life, unable to talk. Unable to make any friends - he learns by staying hidden and watching others. But no matter what he does he is destined to be alone.
So I can understand his desire to have a friend, a companion, a lover. OK, so his reaction to Victor's refusal was rather OTT. His accidental murder of Victors younger brother was unfortunate, but set off a chain of events that only spiralled out of control.
It was only at the end that he realised what he'd done, driving Frankenstein to exhaustion, madness and ultimately an untimely death. His life wasn't worth the pain and anguish it had caused.
Revenge is an irrational thing and both Frankenstein and his Creation became it's master.