The pilot performed a straight-in approach to the north, in calm winds, to take advantage of the uphill slope of the grass runway. He applied 30 degrees of flaps incrementally during the approach. During the landing flare, the airplane touched down, "ballooned up," and the pilot "kept the flare going" before the airplane "slammed" onto the runway, separating the nose gear and bending the empennage downward about 45 degrees. The pilot reported that there were no mechanical deficiencies with the airplane.