The most important aspect of game design

I think you have to remember that you're making a game. It might have a great story, but games aren't just about telling a story. The gameplay itself has to be fun, engaging. But "make it fun" isn't an aspect of game design, its a goal.

You have to break down the problem. Camera angles, control scheme, player abilities... all have to work smoothly. But the development cycle is a process. A game will be ugly, unpolished, poorly balanced or just incomplete for much of it. Early gameplay models might be terrible, but that isn't necessarily a reflection on the final product. I think the most important aspect of game design is simply refining the gameplay. Make sure every element is developed properly so that you're left with something worth playing.