The one thing about human nature I would change if I could is this: I'd eliminate all our selfishness and thoughtlessness and pride, and replace them with love, compassion and humility.
After all, why do we have so many problems? Why can't we get along? Some people say the answer is to change our outward circumstances -- to eliminate poverty, for example, or do away with social injustice. These are noble goals, of course, but by themselves they won't solve our problems, because the real problem is inside us -- within our own hearts and minds. Greed... selfishness... evil thoughts... jealousy... envy... lying... all these come from within. The Bible says, "What causes fights and wars among you? Don't they come from your desires that battle within you?" (James 4:1).
This is why we need God, for only He can take away our selfishness and replace it with His love. And He will, as we open our hearts and lives to Jesus Christ. We can't change our human nature -- not in any lasting way. But God can -- and He will as we submit our lives to Him, because He loves us and has the power to change us by His Spirit.
Is this true in your life? Or are you still struggling to become a better person on your own -- and yet constantly failing? Don't stay on that path any longer, but by faith turn to Jesus Christ and discover the joy of His life-changing presence and peace every day.