Keep working!
~ Animation/Graphics ~
It's really not bad for your second work. The animation and graphics weren't bad. A little bit of room for improvement, but I think you have a good start here.
What I think is obvious is the need for backgrounds in your submission. Detailed backgrounds would add so many good visuals to your submission. Looks like you might have the talent to do it so I highly recommend it. Nobody really likes to see a simple white background in submission like this.
~ Story/Content ~
I liked that you used the slow down on the bullet, but I think that you might have used it too many times. I think that you don't want to repeat animations too many times and using the slow down for the bullet both times was a little too much.
You had a little bit of humor, but nothing spectacular. Really seems like the generic stickman submission. Next time work in some plot or storyline. If you just want to go with random killing then I suggest you make it about a minute or two longer.
~ Audio ~
Sound effects were alright, but again hearing the same splat noise again and again just didn't sound good. You'd expect a different noise every now and then.
I think some nice ambient background music would have gone good with this. Something that sounds like battle music or just pump up music.
~ Overall ~
Other than what I have suggested I would also suggest adding a preloader/play button, replay button, etc.. The basics. I also would like to say keep working because you will improve. Good luck in future projects and keep working hard!