There's a Metroid-like vibe I get from this, and your synths do sound marine, including the percussive ones. I like your choice of instruments; however, docking one star because the balance and reverb seem very much out to me.
The melody, for instance, could use a little wetness to add to the whole marine / ethereal / otherworldly feel that the Windfish has, and then when those other percussive voices come in at 0:52, they can be toned down a little bit to give way to the melody.
1:20 loses its timing, coming in a beat and a bit early, but otherwise, it seems alright.
I'm not quite sure what to make about 3:15, the dissonance that happens there; I think, like with the percussive bits, it can be toned down a little bit, add a volume envelope for effect. Ending is mighty abrupt. Sometimes, letting things reverberate on their own is enough. <3
I gotta say, I love the feel of this thing. I REALLY do. If I were actually inside the Windfish, this is what I would hear, I imagine. Thank you for sharing this with me. Do the necessary tweaks / balance checks and you should be on your way!