GREAT game!
Probably the best game I've ever played on Newgrounds (although there is the game "Frantic" that you should check out).This game has great graphics and obviously great characters. You should make a sequel, but with added characters (popular and good ones like Edd from Edd's World for example) and more upgrades.
Tip #1: Buy Piconjo and Convict first or else you probably won't have money left after for them.
Tip #2: When fighting the last battle for Convict, the key is to keep moving and jumping around, DON'T STOP MOVING, and do not focus on killing one person at a time, only do that if the guy's almost dead.
Also, when Samurai Asshole is attacking you in the air don't try attacking back but block his attacks.
Lastly, only go for the powerups if they are important ones, as in heal and invincibility (thing that turns you yellow), and maybe weapons.
Tip #3: In the last battle for Hank try focusing on killing one person at a time and also keep moving.
Good Luck!