I always enjoyed their aggressiveness, track your finger around and such.
Oscars are neat fish. Those poor little goldfish don't stand a chance.
I think Oscars are fairly intelligent as far as fish are concerned. Mine always seemed to recognize family members and would come to the glass when we were near by. When strangers approached the tank is would lay on it's side on the bottom of the tank.
I used to play "Sea world" with mine. I would hold a feeder fish over the tank and the oscar would jump up and take it out of my fingers.