First of all, thank you for the compliments.
I'd like to explain the reason for the 4 levels:
I created everything myself: code, graphics, and even composed the music and sound effects. I believe that only for the C64 and similar platforms is it still possible for a single programmer to create an entire video game.
Being alone, I had to balance release time with content, and I decided to limit myself to 4 levels for an initial release.
This doesn't mean that additional levels or a sequel to the game itself won't be released later!