Shadow of Fear

" Target foe and all adjacent foes attack slower than normal for the next 20-39 seconds."

Does this increase the casting time of spells/skills or does it only affect normal hits?

Shadow of Fear only slows down normal attack rate. Skills are used at a normal speed. However, it takes foes more time to recover after they attack, thus they tend to use their skills less often in the middle of a fight, but only if they are actually attacking something. So monks and other casters are generally unaffected by the skill.