I would pay many many dollars for awakening 2 assuming it kept a good ratio of new and old characters.
With Morgan as the new MU, Lucina replacing Chrom and Chrom being the new "resident badass"
The worst part is it would probably be easy. Just make (some) the kids the new main characters and throw in some newbies and parent. Oh well.
The way genocide works is you kill literally everyone. Those murders mean a hell of a lot more when you have protected them in pacifist runs. The "battle against a true hero" means a hell of a lot more when that hero is your favorite character. Same goes for the battle that has become infamous in the fanbase.
You could quite easily enjoy it in any order. But given the choice I would always recommend Geno last. I can't see how the game could be more enjoyable the other way around.
. . .plus a few things will probably make less sense lore-wise but that is a minor minor thing.
also what
@Chris Baker said. it's minor but oh well.