Green’s Dictionary of Slang

1. very good, excellent.

1977		Eble Campus Sl. Fall 4: intense – very unusual or uncommon and pleasing.
1981		D. Jenkins Baja Oklahoma 295: ‘This is really intense, man. [...] We’re talking about a couple of far-out dudes’ .
1989		P. Munro Sl. U.

2. very difficult.

1981		Eble Campus Sl. Fall 4: intense – serious, requiring full concentration.
1989		P. Munro Sl. U.