Fetching details from the dictionary...

terrific; staggering; tremendous; incredible; extreme
frightful; ghastly; horrific; terrible; awful; gruesome; eerie
もの凄い量の雪が一晩で積もった。
A tremendous amount of snow piled up overnight.
花火大会の人出はもの凄かった。
The turnout at the fireworks festival was staggering.
この程度の渋滞ならもの凄くないだろう。
Traffic this light probably isn't that extreme.