What can I say? These are some great games.
I've had previous experience with all of them beforehand, although only had previous full-game experience with Zero 3 and 4, and the ZX games. As a whole, I've been playing the Zero series with save-assist. This puts checkpoints throughout the levels which act as reload points, functionally replacing lives and ensuring that, when scored at the end of a mission, you always have 0 deaths regardless of how much you died.