This is a lot of fun, and I really like the art style of it. Great sound and feedback with the gun and like the kind of defending of the bridge to see how long you can last.
While for most of the game you can simply hold up, it might be a fun mechanic if your character moves up automatically and forcing you to balance your shooting speed or else you fall back over the edge working sort of like a timed reload and seeing how close to the edge your willing to get to get that last shot in.
Overall I had a lot of fun with it, managed to get 98, might have to come back and try and break 100 sometime! Don't know what those pink things flying around where but they did manage to add a nice freaky vibe to the proceeding. Great work!