How do you say the expression "Great!" or "Thats Great!" in spanish?
There are so many ways to say something like that, and a lot of it would be regional.
I would say
¡Genial! = Great!
¡Qué genial! = That's great!
You could also say; íQué estupendo! o ¡Qué maravilloso!
= That's wonderful/marvellous!
I hope this helps