Suppose we walked into a room and witnessed this:
"Tommy, pick up your toys."
"Which toys, Mom?"
And without another word, mother sent Tommy to his room for disobedience.
We'd think this mother too harsh.
But suppose we entered the room an hour earlier when she gave Tommy a loving hug and asked Tommy to pick up all his toys... or thirty minutes later when she reminded him he needed to pick them up before company came... or fifteen minutes after that when she told Tommy she'd punish him if his toys weren't picked up soon.
Instead of seeing her as harsh, we'd consider her patient - too patient.
We'd see her requests as reasonable and Tommy's reactions as rebellious.
When people call God harsh for destroying whole cities in Old Testament times, punishing sin in the present, or sending people to hell in the future, they base their opinion on the end of the story, not the whole story.*
In all cases, God is exceedingly patient. He gives us more chances than we deserve (Psalm 103:8-14).
* For one example of God's patience and willingness to give men more chances, read the book of Jonah.