Shiny Pokemon that are only a shade darker or lighter than their normal forms.
I've been considering doing some shiny hunting, and I've been scouting out targets. In my research, I've found so many shiny Pokemon that seem afraid to deviate from their initial color scheme. We need more shinies like Shuckle, where the color change is blatant yet the colors still fit the Pokemon, and Slugma, where the color changes actually reflect another quality the Pokemon could be related to, in this case hardened magma.
Using fifth gen as an example, we have the Oshawott line, all 6 elemental monkeys, Basculin, all forms of Deerling and Sawsbuck, and every Pokemon of every form in the Kami and and Tao Trio that, if I was just looking at one without a comparison, I wouldn't be able to tell which was shiny and which wasn't. Heck, after looking over all of the fifth gen shinies, the best ones are Genesect (who's event exclusive), Haxorus (whose shiny form is given away), and Garbodor.
Some shiny forms are unique, but just plain ugly. Things like a green Ursaring and a salmon-pink Absol are just straight-up hideous. In Gen VI, I really hope they spend more time making shinies look appealing.