Game is lacking the most basic of polish. It needs to be fixed or removed.
* Menus are a mess.
* Upgrade requirements unclear. If it's one upgrade per level, why not just make it automatic?!?
* Upgrade benefits unclear.
* Enemies are the same, bar HP.
* Levels are too short, tedious and buggy.
* Enemy death sound is grating.
* Gattling gun (first upgraded weapon) feels like a salt shaker.
* Sound is buggy - machine gun sound still playing on upgrade screen.
* No penalty/incentive for accurate shooting so spamming is fine.
* Ads also get in the way but are not detrimental. That is until they froze the game and forced me to restart.
* So add: No level select. Had to start from scratch.
PROS
Music is nice.