Well, it seems that hammering the buttons randomly all the way through the level is the way to go to defeat Ben-K. How rubbish.
With him out the way, I then had to fight him again – properly this time – and he was pretty easy. As was the girl I had to play a proper guitar to after that. Now I’m onto some skeletons, who start off like Ben-K (only the cues actually match the music this time, so it’s much easier), and then you have to defeat them normally. I got to Final, but didn’t manage it. I couldn’t time the short “strum” cues that came in a fast stream and so died. Boo.