Controls are tight, but not sure if that's a good reason to have depth charges that insta-kill you right in the first levels. Also, I was unable to collect all the oxygen. the level just abruptly ended as I popped the last bubble. If you're going to grade a players performance based on how much oxygen from the total they can possibly get from the level, then you need to make sure that it's possible to collect all the oxygen before the stage ends.
Music and visuals conveys the ambience without being too distracting or jarring. However, the music loop is not perfectly seemless.