Well, he is one of the most iconic movie villains of all time. I think even non fans know who he is.
Where I thought Episode III goofed was in not giving us enough Vader. He was front and center in the ads, and photos like these were a tad misleading.
We only got Vader in suit for mere minutes. But that ship has sailed.
There is no way to have him living in the sequels, without undercutting the events of ROTJ, and pulling a retro continuity kick to the nuts worthy of Marvel comics.