Fun in theory, horror in reality.
No one is going to hold the 'K' button for one hour, lets be honest. Most of those who do earn the medal legitimately will use a heavy object and place it on 'K'.
The only minigames that seem remotely fair is the Big O and The Pianist, since those require somewhat of a strategy.
The rest only require time. I don't see how waiting is any fun, so I had to give it a rating of 3. Nothing remotely interesting and a game that one could ignore without feeling any sense of regret.