ichii_1 said:
On another read, it looks like kenpachi is about to open a 3rd eye like aizen did :O
So this might mean he's not at that level of power yet and dangai Ichigo not transforming into a monster means he was using pure quincy power.
We could argue about this for days, but the safest assumption is that their transformations are just different in nature.
Kenpachi managed his transformation through natural talent, while Aizen became some weird WTF creature through a magical make a wish ball.
On another note, he should have bitten off Gerard´s ear, that would have made the chapter a 5/5.