SImply put, this game was not fun for me. I liked the artwork and the music, but the difficulty completely killed it for me (no pun intended). It seems that many developers these days, this developer included, don't seem to understand that constantly dying and repeating the same 5-15 seconds over and over again just isn't fun. It's frustrating, not fun. If/when you finally make it past such a point, you don't have a feeling of accomplishment; you have only bitter resentment toward the developer for making the task so difficult.
As others have pointed out, you have no weapon (thus no way to defend yourself), and the enemies anticipate your movement. Worse than that, they can (and will) hit you multiple times while you're mid-air, and you can't do anything until you land (at which point, you're usually dead). When it takes only 3-4 hits to kill you, getting hit 2-3 times during one jump pretty much seals your fate. And when you have several enemies shooting at you from the air, several enemies shooting at you from the ground, and nothing to use as cover to shield yourself, you will die very quickly, over and over again.
LIke others, I uninstalled this game without completing it simply because this constant cycle of get-hit-in-mid-air, die, repeat pushed me beyond mere frustration, and it wasn't worth continuing. Playing games is supposed to be fun, and for me, this wasn't fun.