Kane has always been one of my favorite pro-wrestlers since he made his debut as a masked Big Red Machine Monster. However if i had to pick which gimmick i liked more - I'd pick his unmasked character and here's why.
Yes, masked Kane is soulless and a monster. He also brings an eerie presence about him whenever he enters the ring. Masked Kane showed no emotion whatsoever which was great for intimidating pro-wrestlers in the ring. Nevertheless, he was a static robot. He had no dialogue and no way to show his character. When Kane removed his mask, we saw the monster beneath.
We could see Kane's body just a husk of the human he used to be. His screams were booming loud and utterly monstrous. He had a wide range of emotions from sadistically joyful to full of rage to afraid and so on. A monster doesn't always have to be invincible or without emotion. A monster can take the shape of a human and use those emotions to unleash hell on others. Unmasked Kane had the most sickest and twisted promos as a heel. He was also very skilled at inspiring disgust and fear among fans.
Unmasked Kane is far more perverted than masked Kane because he takes great satisfaction in inflicting suffering in others. Unmasked Kane was surely more destructive. Masked Kane could never reach the heights of Kane when he was unmasked. Perhaps if masked Kane had a manager to compensate for lack of speech during promos then maybe. However masked Kane would be very limited as a character.
This is my opinion of the matter but i ultimately feel that Kane's character has evolved during his time in the WWF/WWE.