Currently, the crenelations on castle walls are significantly higher off the pathway than those of stone walls. This, combined with their additional height, makes it very difficult for a male character (and even more so a female character) to see and shoot over them. They should be lowered and their bottom edge should be beveled to make it easier to actually use the walls for defense.
Castle walls with hoardings have less of a problem here because the shooting slits are taller and they provide murder holes, but a bit more depth on the shooting slit would still be nice.
Castle towers and gatehouses are virtually impossible to shoot out of unless your target is hundred of meters away, making them verge on useless. They also need bevels on the bottom edge of their shooting slits and lower crenelations on top.
This problem makes Castle defenses significantly less useful than Stone - their only advantage is that they soak up more damage, but trading this for defendability is a rough choice for a building that is significantly more expensive. The currently used solution to this issue is placing benches against crenelations where you'd like to shoot, but this is time consuming, not particularly effective (esp for female characters), and shouldn't be necessary in the first place.