Many years ago, an alien race from the farthest reaches of the Galaxy has sent Naju, a planet-sized celestial entity, to the Earth. Essentially it was a colony spacecraft filled with the lifeform samples for us to contact and study, but it has gradually become a giant Pandora's Box when all the inhabitants were struck by mysterious infection. As a defensive measure, Naju was equipped with self-destruction system sealed deep in its corridors, but no survivor has succeeded in activating it. Sent by Terran military, the gynoid soldier Miria (titular Guardian) will have to infiltrate Naju and launch the sequence before it orbits our planet.
After destroying the defense barrier and stepping into the Labyrinth, Miria finds a message from the last surviving creature, Lander (Compile's mascot of the Zanac fame). He briefly tells her what happened to this place and instructs on how to activate the self-destruction system. To do so, she'll have to travel between several Corridors to break the Security Seals. When the last one will be removed, the whole place is supposed to go down.
The Guardian Legend is the first and only, to my knowledge, game that has successfully combined intense and aggressive shoot 'em up gameplay with sophisticated storyline and Zelda-esque exploration and RPG elements. Most of the time you are wandering around the Naju overworld, so-called Labyrinth, battling the inhabitants and collecting new weapons and powerups. There are also traditional shops and password checkpoints, complete with the spots that get blocked whenever you enter, resulting in a midboss fight. To stand against the evil planet, you have an arm cannon and assortment of secondary weapons. Overall, in the usual Compile design fashion, your arsenal is HUGE. After building up enough firepower and health gauge, you'll have to solve a simple puzzle to unlock another Corridor, and after the awesome cutscene of Miria transforming into a fighter spaceship, the game shifts to overhead shmup. The gameplay is pretty traditional here, with each Corridor ending in a ferocious boss fight. The bosses themselves are recycled several times, but counting the limited storage amount of NES carts, that's understandable.
The graphics and animations are perfect, crisp and smooth. Each Labyrinth and Corridor has its own visual theme going on - jungle, ice, volcanic, urban, underwater environments are instantly appealing and successful in setting their respective mood. The designers made a great job creating such variable landscapes. Each portion of the game has its own song, and the whole soundtrack is rock solid, from the symphonic intro to several sound effects carried over from Zanac, the most famous Compile shooter, and one of the spiritual prequels for The Guardian Legend. I especially like the layout and music in the lava world, because it's so dark and uninviting, much like Norfair in Metroid.
Actually, there're a lot of similarities between The Guardian Legend and Nintendo action franchise. Both star female protagonists with cybernetically enhanced bodies, both heroines are able to transform into things, and both Samus and Miria are totally alone in the open world, forced to explore everything on their own and take down bosses five times their size. And to be quite honest, both games are masterpieces of NES action.
The Guardian Legend at time is quite difficult, but not unforgiving. Of course, the shooter stages are quite a hard candy still to this day, which indicates that they have stood the test of time successfully. The overworld portions are easier, but this is compensated by gigantic maps and respawning enemies - overall, this game takes pretty long time to be beaten, especially by NES standards. It's deep, complex and structured, like a great Action-RPG should be.
Overall, at first glance The Guardian Legend may seem to be yet another 'forgotten gem' of the NES library, but thankfully, during the last couple of years it has started to gain the reputation it deserves, being constantly referenced in numerous 'Top ## NES games' lists. This is a good thing, because when it comes to retro games, you gotta respect your elders. And Miria is the aunt to all modern action game girls-with-guns.