2008-05-10 (updated 2013-08-07)
Samus is a Space Hunter (bounty hunter) and she's out to kill the Mother Brain who leads the various Metroid on planet Zebes. Explore 23% of the planet. Shoot anything the moves and a few things that don't. Find all the alien technology and use it to defeat the Mother Brain. Some areas are horizontal scrolling, some vertical. This game allows non-linear exploration and progress.

There are multiple endings depending on how quickly the game is beaten. The endings can be summed up as: Samus is ashame d of you (because you were so slow), Space Suit Samus, Helmetless Samus, Leotard Samus, Bikini Samus. No, there isn't a nude Samus ending, she isn't even allowed to show her bellybutton (which is usual for videogames). However, the Famicom version features a different Bikini Samus in a much, much smaller Bikini.

The back of the box falsely claims there is a 2 player alternating option. The FDS version saved progress in files on the magnetic FDS disks. The development team wanted to use save RAM like Zelda. But Nintendo would not authorize the added expense because FDS Metroid had not been a big seller.

First game to use passwords for game saving?

There is a famous code that for this game:
JUSTIN BAILEY
------ ------

(The bottom line can also be 12 spaces for a slightly different result)
that sparked lots of debate as to who this person was was. S/he was not a creator of the game, and employee of Nintendo, nor the winner of a contest. It was said that "Baily" was slang for a swimsuit and the password meant "Just in a Swimsuit". But no slang in any language uses this term to refer to a swimsuit. Also, Samus is wearing a leotard and never plays in her bikini (see multiple endings above). The password is a normal one that doesn't violate the password CRC, it could not have been specially coded into the game. However, the entire password system could have been coded to make this particular name valid. Giving that the password system was algorithmically generated from a series of incremental values, this is very unlikely. Another reason this is unlikely, is the fact that the following names are also passwords that are CRC validated:
000000 000020
000000 000020
. And finally, there are a lot of valid passwords. In fact there are 126,380,652,742,080,975,503,566,526,109,352,707,862,854 valid passwords (1 in 256 of the total possible entries). Out of all of those possibilities, there bound to be a few names, words, phrases, and significant meanings. Maybe even a line from Shakespeare (someone start the monkeys pressing buttons on gamepads).
A lesser know password:
NARPAS SWORD0
000000 000000
is hard coded into the game and bypasses the CRC. Is has numerous effects that cannot be achieved with normal passwords, such as infinite life, infinite missiles, and the Particle-Ice Beam (the Ice Beam that shoots a blue particle from the Wave Beam in a straight line). What this password means is a mystery, and it probably has nothing to do with someone named Narpa. Note than "password" in a substring of the password. This still leaves mysterious letters unresolved. "Not a real password", "North American release password"?

Other interesting passwords are
Daniel Daniel Daniel Daniel Freeze beam, start in Varia, bombless, bad ending.
XXXXXX XXXXXX KKKKKK KKKKKK Not any equipment at all Start in Tourian with nothing (can't win).
------ ------ 86NINT ENDO-- 4 tanks, 42 missiles.
999999 999999 KKKKKK KKKKKK No time limit, no Mother Brain, no Varia.

Similar to Legend of Zelda, you can actually access your password at any time without dying. Pause (press START on controller 1). While paused, press Up+A on controller 2.

The Japanese spelling of Metroid is メトロイド. But you won't find it as a title in this game entry since Metroid was not released in cartridge for in Japan. There is only the Famicom Disk System version for the Japanese market.