Considering it's your second animation (assumably ever) This actually has some real potential. I'm normally not for the mindless violence thing, but this is zombies... ZOMBIES. I mean, who doesn't like zombies and night of the living dead kind of stuff?
That said, I'd like to offer a suggestion or two to help you out. You're going to find a lot more fluidity to the movements if you add frames. I know, it's a lot of work... Well, animation (much like any art) is not for the faint of heart.
Of course, once you get things fluid enough with the additions of frames, how to make a knife attack or even a gunshot look believable... It seems this is in tweaking your frame-rates... Yes, that too means a lot more work since you'll have to add frames to everything else to balance the whole thing. The fact is (sadly) there just aren't too many shortcuts in animation. I've already dealt with it so I rarely animate something unless I'm absolutely sure it's something worth the bother. But... that's just me.
I think honestly, you're gaining ground as much as momentum, but those suggestions are probably where you'll find the maximum improvements for the minimal adjustment in yourself and your style.
Only hoping to help.