The controls are fine, just as the graphics, but I would insert one colour to that grey. They have their details and it works well, but it's feels, just if there was no life in that game.
Add the number of games, since nearly everyone quits after having all upgrades and that's after wave 10-12. The gameplay itself isn't really that addicting, it's more the whole concept and the possibility to upgrade.
Also there's no need in adding a story.
Oh and add some "special upgrades", like a splitting torpedo or something like that.