The Guardian Legend was released in April of 1989 by Brøderbund and developed by Compile. It is actually a sequel to an MSX game called Guardic released in Japan only. In Japan, this NES version is known as Guardic Gaiden.
The player controls a female "Guardian" sent to intercept a huge space station called Naju on a collision course for Earth. Naju was full of alien ambassadors to Earth, but something has happened during transit and warped the aliens onboard Naju. The Guardian's job is to travel along the surface of the station opening "Corridors" and defeating bosses in several labyrinths. Once all these have been disabled, Naju will self-destruct and the Earth will be saved.
The gameplay is a mixture of open area action-adventure and top down vertical shooter. The surface of Naju is basically an overworld with minibosses placed throughout.
The overworld gameplay is very similar to The Legend of Zelda, with a top-down perspective and the map sectioned off into a grid, with each section of the grid being one screen in the game. Traveling between rooms is a matter of walking to the edge which would cause the screen to scroll to the next area. Unlike Zelda, the game's combat is almost exclusively focused on shooting.
There are several labyrinths which require a key and then a simple puzzle to enter. These labyrinths played similarly to the overworld, where the character is in a humanoid form, walking on the surface.
The Corridors, like the labyrinths, required a key and/or some puzzle solving, but once the corridor has been entered the character would transform into its "space ship" form and the stage would play like a vertical scrolling shooter.
The player can acquire "chips" which improves the basic weapon and can also collect other secondary weapons that functions for both the action-adventure and vertical shooting sections of the game. The secondary weapons range from new various kinds of blasters, to grenades, and even a couple of takes on the lightsaber.
This combination of multiple genres was fairly revolutionary for the time with Blaster Master being another game noted for this type of combination. The Guardian Legend's gameplay may be summarized as a child of The Legend of Zelda and 1942.
The music for the game was composed by Miyamo Shant who also composed music for Zanac. The game has over 20 original musical tracks, which set the mood for each level. Some are more upbeat, some mysterious and slower. For fans of the NES cover music scene, songs from The Guardian Legend are worth checking out.