Its fun! it definitely has the engagement factor, it feels decently fair and rewarding.
Here are some thoughts:
*The main mechanic of the game is jumping/evading (shooting is just mashing since powerups are time-based). With that in mind, I think the bullets of the machine-gun elves could be slower, even if they dealt a little bit more damage, one could at least feel the possibility of jumping evading them, whereas right now it hits almost every-time (at least for me)
*The next step, graphically wise, could be improving the background a little bit; the lines give a fun fake parallax feeling, but those mountains, with only their edges lit and shadowed, look quite flat.
*Perhaps also changing the colour of the sky every level? You could throw in a quick subtle gradient to give it, again, more depth.
Overall, good job! The weapons effect are quite substance-full and I will definitely be trying to improve my score next time.