My love for Bubble Bobble has waned a bit over the years. I play the arcade version sometimes with my daughter. It's still a fun game up to a point, but some of it is just annoying. Anyway, the C64 port is a really good one.
Hysteria is a weird one as I bought it on release and still have it, but can't really remember it at all, even after watching a video. Isn't age a wonderful thing?
Destructo and Clean-Up Service are two I also bought and remember enjoying both. My C64 is out of action at the moment, following a house move. I'll have to dig some of these out when I'm up and running again.
Edit: Actually, I bought (and still have) Frenesis too but didn't get on with it. I think I bought it because it was created by Tony Takoushi who used to write for C&VG.