Galaga is about as basic, and almost as fun as old school games get.
The gameplay in Galaga is simple to learn but hard to master. You move left and right and you shoot. You can get power ups and the enemies become more and get tougher as you progress through the levels. The game gets a whole lot tougher. The gameplay is very fun, and very playable in Galaga. There are no real problems at all.
The graphics are still exact same as the arcade hit before it. Nothing has changed. The graphics were great on arcades and there still pretty good after being ported onto the NES. Maybe backgrounds would've been nice but it doesn't affect the gameplay. The music in Galaga, well there isn't much to it. There are some sound effects though.
Galaga will have you coming back to it for a long while. A great choice for NES owners craving some arcade action.