Think of it like your fav. Sunday morning cartoon. There must be enough elements for the audience to relate to.. same characters, same color schemes, same concept, same voices…
But there must also be a different enough for it to be a brand new adventure… different places, different plots, different goals, different times.
If it’s completely different, it’s like watching a new cartoon altogether. The imagery built up in the audience’s mind that makes him/her want to come back and watch it again… is lost.
Completely same and it’s like watching the same episode twice.
There has be a little bit of sameness and a little bit of difference..