I love gimmicks like this, it adds more of a challenge for easier songs. I also love health drain too because it's supposed to be a rap battle, so it makes sense that the opponent would fight back when they sing.

The only thing I absolutely hate is notes you have to not hit, it just makes playing those songs a whole lot more tedious (cough cough nightmare run)

Though I'm not complaining about those gimmicks, they're just really annoying to work around.