izvanredno

1. outstandingly; excellently
   Izvanredno si odigrao današnju utakmicu. — You played outstandingly in today's match.
   Kako je bilo na koncertu? Izvanredno! — How was the concert? Excellent!
2. (before an adjective) extraordinarily; exceptionally
   Ovo je izvanredno važan sastanak za firmu. — This is an exceptionally important meeting for the company.

For "unscheduled, emergency" Serbian usually uses vanredno (vanredno stanje).