Nice is an adjective meaning ‘pleasant’, ‘enjoyable’ or ‘satisfactory’:
Have a nice trip!
We had a really nice meal. Thank you.
When we use it to talk about someone, it means ‘kind’, ‘friendly’ or ‘polite’:
It was really nice of you to call me.
Tanya’s new boyfriend is so nice.
Sympathetic is an adjective used to describe a person who shows that they understand and care about someone’s suffering or problems, especially by what they say:
My colleagues were so sympathetic when I was ill.
As a teacher, you have to be sympathetic to the problems of your students.
We don’t use sympathetic to mean ‘nice’:
Our new teacher is really nice.
Not: Our new teacher is really sympathetic.
His small house was nice and warm.
Not: His small house was sympathetic and warm.
