Awesome

Formidable – difficult to deal with or overcome
Difficult
Tough
Daunting
Intimidating
Formidable – inspiring respect or wonder because of size, strength, or ability
Impressive
astounding
Awesome
Amazing
Formidable – causing fear, dread, or alarm
Alarming
Frightening
Dreadful
Fearsome
Redoubtable
Terrifying