Originally Posted by
A Chozo
N'Zoth was the weakest, but he knew that, in the long term, losing against the others in combats would work out - the others, being bigger threats, were dealt with first. When he talks with you, it's like a normal person having a conversation. He didn't told Azshara that she would only find ruin, or that her heart would explode - no, he made her think that she would be magnificent. A Queen.
Meanwhile, C'thun only attacked when he felt the Qiraji were ready, and with large armies. Being cruel, brute and precise. Short of words, but a Old God of action. A bit shallow. Even the way you find him is like that: In this small corridor, you turn left there, you turn right here, and suddenly, you are in a room with him.
Yogg-Saron, the loudest, simply bent the will of whatever he reached, putting in motion whatever plan he could put his tentacles around. Emerald Nightmare? He sparked it. Saronite for the Lich King? He provided it! Influencing Loken, impersonating Sif, even (for some reason) creating that weird avatar: Sara. In the fight against him, we managed to see lots of different plans - especially the Dragon Soul plot.
Now, Y'shaarj, he was the mightiest. And even after his defeat, he managed to create chaos - not by crushing mind-bending, no. He just needed to make someone angry, or someone doubtful, and things sorted itself out. Being only a beating heart, he did his best to give Garrosh the tools - his blood - to create chaos.
And, even if Xal'atath isn't an Old God, she also demonstrated personality: resentful of her demise. Feeling cheated. But she waited, patiently, being passed from hand to hand, until a worthy one came: The High Priest of the Conclave. The final tool of her vengeance.
...But sure, if you think Illidan's return was a well-done story, it makes sense that you think that Old Gods lack potential and personality.