I am stuck too, I have bought every weapon and pwned a lot of enemies on each standard level, I don't understand how to unlock the others. No one knows?
Another tip: Reload the shotgun right after you shoot the first shot. The cooldown between reloading and then shooting is shorter than between each shot.
My tip: Jump. It will save you many a time and doesn't seem useful until you try it. Other Tips: The UZI is basically useless, you're better off with the rifle. The Bazooka overheats Reload the shotgun frequently Bananas are good as long as you don't hit spikes or bombs afterwards Don't die Whenever you reload the shotgun picture he's playing the guitar. Makes the game funnier.