The Justin Bailey Code in Metroid is a total fluke, according to the Metroid Database. That code gives you Leotard Mode, with all the items but one energy tank, more missles than you could carry, and the Wave Beam rather than the Ice Beam.
A better code is NARPAS SWORD0
000000 000000
You can't die, every item, both Ice and Wave functions (makes a thicker Ice Shot), and unlimited Missiles. You need to kill Ridley and Kraid, and your timer is 00:00.
You can die of the self destruct, and saving the code will give you 5 missiles, and 30 energy when you quit and return.