Difficulty level of this game is high because it is very tricky and when you get stuck, 30 seconds ad for a hint and another 30 seconds more to get to the actual answer. I did a couple of them, by the time I got to the doorknob, even when I already saw the actual answer by the time I applied it, it still took me a couple of try to open it.
So I am surprise that people are giving this game 5 star rating.