Ooooh, this is fun. It's a great game, I like it!
Some problems in my opinion.
Movement feels slidy, making it hard to control. It's probably because it's grid based. I think it would better if the grid steps were brought out better through animations. So the player doesn't move in a linear speed but each step starts fast and ends slowly easing into the next tile.
The oxygen mechanic feels a bit pointless as you could remove it from the game and it would still be a game. So the theme is a bit of a miss in my opinion.
Other than that it's a cool game with a lot of potential for challenging levels. Maybe lose the grid movement and it could be a full on rage game kinda thing.