I'm level 50 now, and I'm starting to think how I'm gonna realize this was such a waste of time after getting all the stuff.. Well, it's voluntary, so I'm the weird one here, not the game.
After a while of playing this, all I could think of it was "Meh."
At first it feels like it's just clicking the mouse button until you break your finger, and once you get a little further, it's just jumping backflips and spraying bullets at a mass of enemies. Tactics or skill aren't needed or used, as you'll get bulletraped once you stop backflipping for one second. I'd give it 2 and a half stars, so I'll just leave it without a rating.