This isn't a bad demonstration, but if this can stand on its own then I think it needs more.
Every time one gets shot and the level resets, the stage is exactly the same, every time. The characters may as well not even die, just keep shooting at each other with no effect.
Plus there's no music. I don't know if that's really such a big drawback for me but I know that can make it harder for others to stay engaged.
Also, if this is meant to be played by two different people at the same time, then the controls shouldn't be so close together; they'd have to use the same arrow pad at the same time, or use the numbers I guess but that shouldn't really even be required - ideally it could've been some keys on the other side of the keyboard. And hitting up and down always makes the screen scroll up and down which can be a problem while trying to play.
And I guess it could've had a score keeper somewhere on the screen to at least make it more competitive.
Like I said, it's a good demonstration as it shows you have a general understanding of coding and that there isn't really any functional problems with the game itself like the controls all work and everything in the game works as it should, other than maybe the screen scrolling thing, but this game could definitely use some work as it does have a lot of potential. It's a work in progress! :)