I visited Great Falls Park (Virginia side) during October 2003. There are several wonderful overlooks near the main visitor center. In that general area the path is a wide level path with room for picnics and other activities. As you walk down the trail it narrows and has some scrambling but is an easy trail to hike. Through the woods I often had views of the river (leaves had already started to fall as the season changed).
I only went a mile or so on the trail and the traffic on the trail was high the whole way (a weekend with decent weather). It was a fine walk but not really a great hike, in my opinion - the falls are spectacular.
More Washington DC photo essays: Botanical Garden - Shenandoah National Park - Library of Congress - Great Falls National Park - C&O Towpath (Monocacy Aqueduct) - Bull Run Trail - Bull Run Mountain Conservancy Trail