My understanding from listening to some guy on the radio, almost certainly on NPR, is that's a fairly modern conception. It's like they couldn't put the Christ back into Christmas, so they shoehorned St. Nick into Christ instead.
"For God did not send his Son into the world to condemn the world, but to save the world through him.". John 3:17
Christ didn't come to reward the people already doing good, and punish those doing evil.
Rather, "[...]for all have sinned and fall short of the glory of God, [...]"
People are not justified by being "good enough" by themselves, but rather, are "[...]justified by his grace as a gift, through the redemption that is in Christ Jesus, [...]".
Your description of "You're punished for evil and rewarded for nice and he's watching you all the time?" is, I think, a very misleading and simplistic idea of Christ.
Why would you not include that in the "being good enough" part?
I wasn't just saying that "being good enough" isn't enough. I was saying that no one (except Christ) is good enough. That one cannot, of oneself, earn or achieve justification, but that one is given justification, that one cannot deserve, as a gift.