The ability to hear the voice clip of your character's battle cry (for lack of a better term), aka the sound that they'll often make when initiating most forms of non-magic attacks. Considering that's the voice clip that you'll hear by far the most often in the game unless you play strictly caster classes, I think it's rather important that it gets a preview.

I think the original viera voice 7 or whatever number it was wouldn't have achieved the level of infamy that it did if people could have realized that's how their character would have sounded like in battle before actually confirming it and burning their fantasia.

I'm too asexual to care about the usual boob/butt slider things people are usually clamoring for (or most other physical attributes in a character creator), but ensuring my character doesn't regularly make obnoxious combat sounds is something that's always been considerably more important to me in video games, if that's an option.