astounding
I thought he'd made an astoundingly bad decision, but I was wrong.
Space research took off with several astoundingly successful planetary probes.
He has had an astoundingly successful career.

SMART Vocabulary: related words and phrases

Surprising and shocking
against all expectationsphrase
amaze
amazing
amazingly
astonish
dumbfoundingly
dynamite
earth-shaking
earth-shattering
earth-shatteringly
pull
pull something out of the bag/hatidiom
raise (a few) eyebrowsidiom
reality check
sensationalist
turn-up for the book(s)idiom
unbelievable
walk
walk in on someone
world-shattering