[spoiler:1v8j5jr9]Act I and Cain gets taken out by an out of the blue villain with little character to her, that's just a dumb move, you don't do that.[/spoiler:1v8j5jr9]
[spoiler:1v8j5jr9]My friends and I had a discussion about this. I think it's fitting that he's killed by some random character with little development, because you expect him to have some powerful and fitting death and to go out in a blaze of glory. Instead, he gets cut down by some petty character, really defining his mortality.
Same with your point about Leah, what you suggest is way too cliche and again, shows that she is mortal and is an ant compared to Diablo, a pawn in his game.[/spoiler:1v8j5jr9]