This is one of those games you can just go back to for a bit, then stop for a while, then have another go at and so on. With this in mind, I had a go at the three “open” levels in Hard mode. And failed to complete any of them. I think I need more practice. Which completely negates the thing that I just said just now.
Finally got back into this today, having finished some other games and stuff in the last couple of weeks. And it’s still ace. I’d previously only completed the one level on Hard, but I rattled through about 8 or 9 of them, including “ABC” which I unlocked. I also ranked up a couple of times too, and managed my first Perfect (on “YMCA”). Excellentia.