Cheat: 6 Continue Code
On the title screen, press and hold UP, LEFT BUMPER, RIGHT BUMPER, and press START, START (twice rapidly).
Unlockable: Napalm Weapon
In mission 1, destroy the boss (the power core) and just that enemy. Do not destroy any item containers or other enemies. If you earn exactly 2800 points, you start the next stage with the Napalm weapon, which pretty much kills enemies with 1 hit and most bosses in 10 hits or less.
If you are having trouble maintaining a lock-on while firing, choose one of the control options that locks your gun when firing.