This game has a couple of really cool moments in it. So, the game starts by making those little green enemies pretty easy to deal with--you can just shoot them with your submarine. The first cool moment is when one of them spawns in right as you collect the keycard. You're vulnerable, and you need to get the keycard, but all of a sudden you are in real danger as there's an enemy following you that you can't shoot.
The second cool moment is when there are two of the enemy-spawning-spirals right next to each other, and no real space to back up and shoot the enemies. This is pretty neat, because earlier I had learned to deal with those spirals by backing up and shooting the enemies until they were all gone. But in that part of the level, this isn't really possible, and so I have to decide to just run, instead. This is made even better by the additional spirals that line the tunnel--now I really have to commit to running.
The third cool moment combines the first two--now I have to get another keycard while running from all these enemies. I think I did end up dying here, maybe? I'm not quite sure, as my diver-health bar just seemed to fill up a bunch without any real death indication and then I just won the level.
Either way, these are some really nice moments told through pure level design, and I just love level design like that. Really good stuff.
I have a couple nitpicks with other parts of the game--for example, the audio seems pretty minimal and hard to hear (it's possible my volume is too low or something?) and there are a number of graphical glitches... but I did really enjoy those aspects of the level design. Good job!