I’ve played this one before, within Donkey Kong 64. However, I only played it in the way required to get the Rare Coin and then moved on. It was just an obstacle in DK64 and I didn’t really look into it for its own merits.
Playing it through Rare Replay, and I’ve realised that Jetpac is probably among my favourite classic score-based arcade games. Your goal is simple to understand without needing further instructions: collect parts of the rocket, fill it with fuel, and avoid being hit by enemies. Once you fill the rocket up, you step inside and move to the next screen and repeat (although for the next three levels you just fuel your rocket, then get a new one to build every 4th screen).
The player movement is incredibly smooth, which helps to make it really good fun. Each screen will also have a different enemy type which move in different ways, but you only get one type per screen which makes predicting how enemies will move something fairly easy.
Jetpac is a classic which is overlooked. I think it’s especially impressive that this was limited to home computer restraints, and not the beefier arcade cabinets at the time.
My “completion” of this was to complete all four stages of rockets (the suggested milestone in the game) and completing all the Rare Replay snapshots. The snapshots has some interesting challenges and felt quite fair, I quite liked the simplicity of completing 5 “laps” of the screen.