I think the main problem with these attacks is that there's not enough "oomph" behind them. They're very obviously a punch and a kick, which is good, but they lack that same kind of power that an actual punch or kick would have simply because you seem to be too scared to draw a completely new pose for certain frames (or at least, that's how it comes across). To make an animation with such an "extreme" feel as an attack, you can't be afraid to draw in plenty of movement between frames.
I made a quick edit to your punch to show what I mean
Yours:
Mine:
The two biggest problems I saw with yours were the overall lack of movement in the character throughout the animation, and the lack of any kind of "snap" or "oomph" in the punch, it feels more like he's just pushing his arm out there instead of throwing an actual punch.
Regardless, this is a nice start and I'd love to see how far you're able to take these animations.