What am I doing wrong with my rigged body? I just started "playing" with blender after realising that I have to be able to design my own objects to make my own game without keep on using someone else's work/Unity Asset store prefabs. I never designed anything so, yeah, I can say I'm pretty horrible at it.

Everything was going somewhat fine but I don't know why my character's body is not moving smoothly at all. Could you tell me if I'm doing something wrong please?

Here's a video showing the current issue (I know I can use the paint brush to correct the distorted shapes when I rotate the figure but I'm pretty sure I screwed up somewhere with the armature movement part as it lacks smoothness)

EDIT: Here's a download link if you want to see my file:
Deactivate the Snap option (magnet icon on the horizontal bottom bar of your 3D view).