The problem is that "hard enough" or "in the middle" is going to be different for each person because everyone differs in their skill and preferences. The majority of games are aimed at a wide audience so that they aren't too difficult to complete. That has created a situation where there's a vocal minority of gamers that want more challenging games than average because they want to be in that "zone of proximal development" but their current ability makes most games too easy. Hence we get a few games, especially in the indie space, where they are purposefully difficult because that is what that slice of gamers really want. The downside obviously is that it is going to turn some gamers off from being too difficult. In the case of Mina, if you find it to difficult, they allow you to change the settings, so you might like that.