Speaking specifically of shinies, I really like what Gen 6's transition did to a lot of them with vast improvements to a lot of those terrible colors.
Like Espeon's radioactive jade bullshit it had going on the past few gens which just looked awful, and now it's like nice darker emerald green which goes really well with the red/blue (or you could say ruby and sapphire) contrast on its eyes and gem.
Things like Dragonite and Venusaur are even better in terms of color. They picked better shades for a lot of the pink/green shinies. I hated how yellow shiny Venusaur was.
Things like Gengar/Garchomp's shinies being fixed for their megas are great too.
Color-wise, Gen 6 did a really good job on shinies and that's like the only thing that would've made me disagree with you, OP.
