Dic: intense (one of its meanings) and intensive

• I know he's an intense player, but he does enjoy what he's doing.
• His intensity and the ferocity of his feelings alarmed me.
• an intense look.
• He’s very intense about everything.

1. ADJ | If you describe a person as intense, you mean that they appear to concentrate very hard on everything that they do, and they feel and show their emotions in a very extreme way.
2. (of a person) having or showing very strong feelings, opinions or thoughts about sb/sth
3. characterized by deep or forceful feelings.[Latin intensus stretched]

... Cobuild, OALD, Collins Essenial

Cf. Usage Note: intense and intensive

The meanings of intense and intensive overlap considerably, but they are often subtly distinct.

When used to describe human feeling or activity, intense often suggests a strength or concentration that arises from inner dispositions and is particularly appropriate for describing emotional states:

• intense pleasure,
• intense dislike,
• intense loyalty, and so forth.

Intensive is more frequently applied when the strength or concentration of an activity is imposed from without:

• intensive bombing,
• intensive training,
• intensive marketing.

Thus a reference to Mark's intense study of German suggests that Mark himself was responsible for the concentrated activity, whereas Mark's intensive study of German suggests that the program in which Mark was studying was designed to cover a great deal of material in a brief period.

... Am-Heritage, http://www.thefreedictionary.com/intense