How would you personally define an 'intense person'?
Depends on the type of intensity and whether I saw it manifesting positively or negatively. Most all types of intensity could be either I think. The types I can think of immediately:
outwardly they’re focused, driven, competitive, or the negative end where they’re roided out berserk jocks who can’t take a no and are probably intense because they’re sore losers.
internal intensity means they’re pensive/introspective, probably depressed and thinking of heavy subjects all the time. To the negative end they might be melodramatic, anxious/manic/high strung, or overeager/codependent.