There are enough games that do not have a mute button (@CMLLMC). And even if it is there but hidden, it sucks. Looking for the mute button is almost always the first thing I do when I start a game.
Now it started. As said before, the keyboard input doesn't really work. But the game has a mute button! There are so many game without, I can't believe it, so I give one extra point for that: 2/5
At first, I began with level 5. Then I saw there are also levels 1-4 "to learn how to play". But in level 1 and 2, you don't even see anything, you have won immediately.