We say "sugoi" when we are wondering or admiring
or amazing something or someone.
For example, when I see the Niagara falls,
I cry,'Sugoi!' (amazing! nice!...I feel.)

When my friend finish very difficult works,
I say to him 'Sugoi ne!' (I admire him.)

When I go outside and find UFO (like 'Independence day')
I may cry,'Sugoi! nani? are? '(nani? are =what is that?)
etc...
We often use 'sugoi'