Really fun game, good graphics and gameplay. Once you understand how to dodge the asteroids it's easy to finish, but I admit I died 4 or 5 times before completing the game. Although I think this is already a good game, I think it could be improved; here are my thoughts:
-Running out of oxygen is almost impossible. There are many tanks which also respwan after a bunch of seconds and they refill completely the oxygen bar. I feel like at least one of these things needs to be nerfed to put more pressure on the player and make him more aware of its resources.
-You should make the monster cutscene skippable. It's really good but it gets annoying after 3 or 4 times, so I would put this option to save time.
-The theme is weak, and it's a shame, cause the game has so much potential. Consider adding a cutscene where the monster awakes and attacks the player in the red asteroids section; that's a simple way to fix it and to make things more interesting.
And that's all, your game is overall impressive and one of the most fun to play, so keep up the good work.