The Israeli army issued a statement casting doubt on reseach methods of HRW, asserting that all Israeli forces' combat actions "conform to international law, as do the weapons and munitions used".
Israel said it launched its December-January offensive to counter rocket fire from Hamas-ruled Gaza.
It has since weathered foreign censure over the killing of some 1,400 Palestinians, many of them civilians, during the fighting.
HRW based its findings primarily on debris from Israeli-made Spike missiles, which it said are fired from drones.
But Rafael Advanced Defence Systems Ltd, Spike's state-controlled manufacturer, said the missile, which has been sold widely abroad, can be fired by helicopters, infantry units and naval craft.
Marc Garlasco, HRW's senior military analyst, said they were able to establish that drones fired the missiles after gathering evidence from Palestinian witnesses who said they had seen or heard the unmanned aircraft.
But he conceded that two of the incidents cited took place in the evening or night, ruling out the possibility of anyone seeing the small and often high-flying aircraft.
Asked about the possibility of an armed drone being spotted solely from the distinctive buzz of its propellers, an Israeli defence industry official noted that surveillance drones had regularly patrolled Gaza during the war.
"How could you tell what exactly you were hearing?" the official asked.
The Spike has a range of 8km, Rafael says.