The game has a really nice artstyle and a very simple concept while still being enjoyable. The lack of music is a bit off putting and I would have made the power bar a bit larger as its difficult to spot at first. Otherwise it's really good, congrats on your first game!

That was fun! Really hard though at first, but once you've memorised everything and get used to it it's better.
Would have advised less of an up front commitment though. xD
Well done on getting this done on time!

For a first game, this is quite the accomplishment! The graphics and the physics are very well polished. I have to agree with @dreadloaf that there should be more emphasis placed on the bar, but it serves its purpose just fine either way. You might also want to think about whether you want your game to depend on memorizing the level or something else. Regardless, you have a very visually impressive and engaging game. Keep it up!

Art style is fantastic, gameplay is unique and fun, got annoyed everytime I died and it restarted the whole game, that is my only problem with it. Apart from that, strong game indeed

The art style is great, but would have loved it if there were sound effects would add to the mood a lot. The gameplay is anything special. But its challenging so its ok.

This game has absolutelly beautiful graphics, but I find the gameplay quite lacking. What I don't like about the gameplay is that you're not able to see much of the world around you, which is pretty unintuitive considering you're supposed to explore the world and find the exit. My other problem is that the O2-bar depletes really fast (it does in level 2 - I didn't make it past this level), which is a problem when you take into consideration how difficult it is to find the exit, when you're barely able to see anything but your submarine.

There's no audio, which is a shame because it has potential to have an amazing atmosphere

I really enjoyed this idea, like the others said the graphics look pretty nice and I'm not a fan of pixel art but the your quality is up there. I played in full screen and found it annoying to look at the top left to keep track of my o2, it wasn't that bad since the only other thing I had to do was navigate but I'd imagine you would eventually add some additional mechanics. I don't know if you've played Song of the Deep but that may be a source of inspiration for you. I like what you've done so far and I hope you keep working on it and turn it into a full blown game.

I'm really sorry guys! I wasn't expecting anyone to comment! Thanks so much!!!