“Wow, good for you!”
Your young child shows you a picture he drew of a flower. You say this to encourage him.
Wow, good for you!
This phrase is used to praise small children. It means "you did a good job".
However, when this phrase is used toward an adult, it can seem insulting. It sounds patronizing, like you are suggesting that the person you say it toward is a little kid.
"Good for you" can also seem like a rude way of saying "I don't care." For example, you might say it if someone you don't like is bragging about something:
A: I was the class president of my university.
B: Good for you.
"Wow!" expresses excitement. You say it when someone tells you something or shows you something. You can use "wow" to express a variety of emotions about the thing you're being told or shown:
- it's interesting and exciting
- you want to encourage the person, especially a child
- you can't think of anything else to say