Aliens have captured your ship and it now lays in pieces all around the galaxy, so if you want to get it back you will have to travel from planet to planet, exploring inside a capsule. A tough work, as they are not the most manoeuvrable things, nor the best for fighting back.
There will be two main enemies fighting against you, the real enemies, which sometimes may cover the screen with shots, fighters, big ships, canons or missiles, but normally are easily dispatched, if you manage to control your machine; and the dangerous and constant foe, gravity, continually machinating against you. Fighting gravity is the hardest part, as it requires skill and getting used to how the capsules moves. They are propelled by a motor in their back and can rotate over themselves, so it's like controlling a rocket while continually being pulled down.
Your job will consist mainly in the exploration of the planet, where there will be many things to find and take back to your ship, some for money, others to improve your capsules, and a third kind consisting in fuel, needed to continue to the next place once the last thing has been found, the piece of the golden starship, hidden somewhere in the planet, on its own little map where the automap, if you have one, won't work. Carrying these objects around is not always easy, as you now are controlling two objects joined with a rope, and in some planets the gravity already makes it hard for your capsule alone to move.
To make things, somewhat, easier there are those improvements, apart from the few found, like the turbo for giving more power to the motors in exchange of consuming fuel more quickly; they are bought, a good deal of them are weapons such as seeker missiles (as useful as dangerous, as they may go after you), other are better capsules, and some give interesting improvements to your vehicle. But buying can only be done after finishing two planets.
That leaves you always in the same spot, one shot and the capsule is lost, leaving you on your space suit. Another shot and a life is gone. That can be avoided, somewhat, with the shield, you won't be able to carry objects but you will lose part, instead of all, your fuel with each shot, as when you hit obstacles. But sometimes being in the suit is not that bad, you can not use objects or special weapons, just the map, but it is easier to move around, if you land softly you can walk around, and with a bit of luck you may find one of the capsules that for some reason are abandoned around the place, or go back to the ship before getting killed for good.
As is common in NES games, there is one thing that makes interesting the game, but in a way that makes the game interesting for a long time, the gravity system. It makes the game always hard, but not too hard to be unplayable. But there is something that may make the game somewhat tedious, passwords; there is no save system (unless you use emulator), just passwords.