Wait, what? This looks like a pirate version of R-Type 3 for the SNES...
Anyway, regarding the sound design, I think the songs sound rather lacking because of the missing drums. I feel like they could really use some bass, too. The plain fade-out instruments sound very simple like the Gameboy and beg for more things to be done to them, such as delayed vibrato. The Stage Clear song has some really awful phasing effects and I think it could use some Pxx detuning on it. I'd also change some duty cycle stuff but that's just a personal preference.
I think if you want to check out cool effects you should check out NES Metal Storm by Irem:
it has some really cool boss explosion effects! Interestingly enough, this is the same company who made the R-Type series.