It's just ok, and, if you don't speak German, not useful right now.
If you skim read like me, then you saw the words "in English" in the description. This is a future update for the game. The game is currently in German. If you want to grab it while it's on discount and hold on to it until the update then by all means do so, but be aware you won't be able to play for a little while unless you are multi-lingual or German is your first language. And as you can see from the game thumbnail, it has a somewhat demonic undertone to it. The demonic monster face, the creepy you've just entered a scary amusement park and will never leave alive soundtrack. Graphics are very mediocre, but I hesitate to complain about a free app.