confuzing is the easiest sum up of this game
you tried, but the game it self was more confusing than fun, and more annoying than anything, its really repetitive, and after wave 6 or 7 it just becomes rediclious.....
Make a better upgrade system, such as faster bullet flight, or penetration or even quicker shots all around... the upgrades as is are hard to even tell the difference between levels one and six....