Wow. The first half reminds me a lot of Metroid Prime. Interesting.
Anyway, I think this could have benefited a bit more with other variations in sounds. By the sound of this, I also feel it would have been much better if the main melody didn't stay so consistent, but that's probably just a nitpick. A little extra panning to make a sound or two a teensy-bit distant would have contributed to the ambient feel. Overall, I like what you've done here!