When I watch videos of Grim Dawn I never see the enemie react to hits by your character. Its just like in Titan quest.
Is there no hit reaction in the game?
Hit them with a large enough fireball and they’ll react by hitting the ceiling.
Yeah but when you strike with weapon normal, there is no impact reaction as I can see.
They reacted in TQ and they do so now as far as I can tell, maybe play the game instead of watching low res videos 
Enemies react to hits in a sort of ‘ministun’ if you do a certain portion of their max health in one attack.
Bosses are immune to this.
Enemies definitely react to you hitting them. I’ve bee leveling a couple of Forcewave builds and they do this animation where their upper body gets pushed back when they get hit by it.