As Shift mentioned, you're not bad. All you need is to practise some more. The first replay is quite stiff, it was alright, but the rest of them are not bad. Try working on getting less stiff and use less grab. Also, try not to contract your knee/elbow immediately after you dismember any of the joints. It tends to make the hit look weak and in some cases sloppy.
Remember, practise makes perfect.