Ace custom weapons
The weapon customization was definitely the standout feature of this game, and I loved it, except that it was mostly rather unnecessary throughout the game. Perhaps it was just my fault, stumbling onto the fact that rubber guns set at a very low angle drench the screen in bullets, and are the only noteworthy weapon until the piercing rounds.
What I would like to see to make the system more relevant is weapons broken down into 2 parts: weapon and properties. For example, in the weapon category you could have Machine Gun, Rifle, Cannon, Plasma Wave, Missile, and the like. They would effect the shape, speed, range, and damage of the bullet. Then, customize with different properties, like rubber, piercing, explosive, ghost or whatever have you. That way is I want faint bullets, but like the Plasma Wave, I can have it. If I want a bouncing missile, it's there. Explosive Lasers? Step right up!
Played well, had some fun, if not terribly challenging medals, and was a good time. Keep it up.