I downloaded the Spectrum Parsec image and played it a good bit. Up to level 3 and 50,000 or so points, and I think it's fantastic. Things to note are;
There's a timing issue on some of the sprites that don't fire, such as swoopers, one of them can drop through the bottom of the screen. Mostly to note, the player ship's overheating is a little on the touchy side, you can overheat on level three simply by tapping fire too many times. These are just minor things though 'cos overall it's fantastic to see it on the Spectrum! They did well with the scrolling background.