When I used to have the Level Editor version... I used to made this level long and extremely hard by editing EVERY enemy's bullet speed to be really fast, including the Boss itself. And made sure I included each and every enemy unit in that stage as it's the stage where the main base has to throw everything they got at you.
I noticed this when I downloaded them, they sounded really different on the Windows Synthesizer so I ended up downloading these which are Soundblaster I believe.
@Ebb1993isimmortal i agree, i found the final boss (the demonstar itself =O) to be a pretty big letdown, what i liked was in level 13 how the boss suddenly flies in hurling asteroids at you, its surprised like that that make it fun and hard