It took four years from the release of the arcade version of Darius before this first port appeared on the PC Engine CD. It took only just about a year for Gradius to make it from the arcade to the Famicom, but there isn't much debating that Darius was much more of a challenge technically to port. Its unique three monitor setup and emphasis on the soundtrack almost guaranteed that a port wouldn't be able to hold up.
Naturally that sort of long display setup couldn't be replicated on any home hardware at the time, so the solution was to zoom in the graphics quite a bit, making the sprites bigger but the field of play smaller. The larger sprites definitely look nice, and from a visual perspective the graphics hold up well against the original. The problem is that the game was designed with a wider field of play in mind, so zooming that in and reducing it really has a big impact on how the game plays.