Sure, I can see the softer shading being nice. I find the shading on the horsea to be nice. But I think something is off about the shading on seadra's frontsprite hair. It lacks depth. Perhaps shifting the colors around rather than re-coloring would fix that.
The fan is not really 2D. If you look at kingdra's backsprite you can see the base of the fan. I imagine the idea is something like temari's fan, so it's probably at least as thick as an arm. And most arms require shading. That being said the end part of the fan in frontsprite/backsprite don't match, but that's probably intentional.
Hmm... I still think the lower half of kingdra's face can be more moe. The top half is good though. But perhaps this is just an opinion thing.