Play and Intensity are complementary, not opposed. They support one another ...
Seek, in every moment, to regain the intensity you had as a child at play. Children playing are more intense, more focused than any adult. In your play seek to regain that intensity.
Let the attitudes of Intensity guide the expression of Play.
As an adult, however, you often find that you are more serious and grumpy the more intense you get. Seek to maintain the attitude of play in your intensity.
Let the attitudes of Play guide the expression of Intensity.