Axelay is very high on my list of favorite SNES games, and "Unkai" is a great song to boot. The original 16-bit version is a tune that I have (literally) heard looped for hours on end. On top of that, I have heard several remixes, from different artists, using completely different instruments. So, yeah, I'd say you nailed it. Every single note of it!
Are you planning on doing any of the others? I'd love to hear "Colony" or "Mother" given the 8-bit treatment.
One more thing! Hey, supernintendosp, if you want to hear a 16-bit version of this song, go to Youtube and look up the original version yourself. Dumbass!