I'm bored by the minor "just a spirit in a shape"-type of familiar, because it falls between two stools. It's neither something cool, like an actual spirit, which might change forms (just as the familiars of legend often did), nor something with a bit more solidity and personality, like the "enhanced animal" familiars of old. I think they're also too easy to kill, which necessitates them not causing problems on death, because it could happen from some blowing on them hard. I also dislike that they're generally personality-free by default.
So I'd like to see something where familiars were, by default, actual creatures given enhanced intelligence, where they were quite a lot harder to permanently kill (maybe easy to force out of combat though), where they had more personality and could be roleplayed, but where their mechanics remained fairly simple.
I suspect an awful lot of people who play today would be EXTREMELY UPSET if dear Doctor Fluffykins could permanently die though and their baseline is the 5E approach, so they likely feel pretty strongly about it.