Also, would it be possible to implement a system like in Amphorous+, where one can unlock perks through achievements, to aid high-score attempts? Things that boost the effectiveness of the powerups, which also can be combined, and things that generally make your life easier ( regenerating hp, a shield, ectetc), will really make for a whole lot of combinations, and good material for discussion.
I like the idea of free, tactical powerups that can be mixed and matched. Is it already in effect, that the ghost turret also benifits from your powerups? Like if I used a ghost turret, a penetrating bullets and a rapid-fire, does my ghost share that ablilty? Also, penetrating homing bullets from a frag blast. I love the powerup system.
 "Pursuit of hat"){kind=icon}
 "Diepix Arena 2"){kind=icon}
 "Pigs Can Fly"){kind=icon}
 "I Am An Insane Rogue AI"){kind=icon}
 "Arkandian Crusade"){kind=icon}
 "Ghost Guidance"){kind=icon}
 "Heroes of Kung Fu"){kind=icon}
 "Frantic 2"){kind=icon}
 "Water Werks"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}
 "faze"){kind=icon}
 "Little Wheel"){kind=icon}
 "ROLY-POLY Cannon 2"){kind=icon}
 "Remnants of Skystone Beta"){kind=icon}
 "Spewer"){kind=icon}
 "Crush the Castle"){kind=icon}
 "Days 2 Die"){kind=icon}
 "Tilt"){kind=icon}