Normaly you use that expresion when you are surprise a lot about something in a good way or a bad way. For example: ¡qué barbaridad! ¡consentirle que hable así a sus padres! → that's awful! letting him talk to his parents like that! --> in this case it's a surprise about something bad ¡qué barbaridad! ¡qué bien hablas el inglés! → that's incredible o amazing! your English is really good! --> in this case it's a surprise about something good