It needs some improving.
There is a lot that needs to be done with this. It's not bad but there should at least be a small tune or song that plays in the game. Without this you'll only hear the gun fire. Which can get annoying. It's good that you've added to option to turn it off.
The control screen (Where you read the controls) is really hard to pick out what is what. It seems smeared across the screen. I don't know if you did that on purpose, but I would have a decent little picture of the game while reading the controls.
After clicking play I came across a white bland screen that that had the buttons options, upgrades, and the choice to turn on/off the turrents.
Not enough time was put into making the I guess I would say "pause" screen. It's dull and doesn't really have anything unique about it. Just 4 buttons and a stat box.
I suggest starting with that screen and filling it in. There is too much space left out. Filling in that negative space will greatly improve on the looks.
Instead of white, use more of a metal look to it. Probably input a picture of some kind.
I see nothing too special about this game. The gameplay is alright. I had a little fun, but the graphics need a tune-up. The penguins do look like penguins, just there not well made as the guns.
This game has upgrades, and it has different choices of wepons. It's not that bad of a game. It looks as if you did do some work on this and actually tried. I had some fun playing this and I am sure everyone else did.
Keep trying, and good luck on future submissions.