Another, and more significant now that I come to think about it, difference is that Terra fears the darkness, Riku does not.
I'll have to play the game again to be sure, but Terra seems to be in the same state Riku was during CoM. He can use the darkness but he doesn't really have control of it because he fears it and ultimately rejects it but is overwhelmed by it. Riku fears the darkness at the beginning of CoM but he accepts it an ultimately masters it. The only other person in the series who seems to have truly mastered the Darkness is Master Xehanort himself.
Thus instead of being more like Terra, Riku is more like MX but not corrupted by his power. Terra is the wholesome, powerful, but naive hero that was betrayed by someone he had blind faith in, thus he is more like Sora.
Plus, while Terra fueled the desire, it was originally the story about the "kid who traveled to other worlds" (MX?) that sparked Riku's wanderlust.
I'll have to play the game again to be sure, but Terra seems to be in the same state Riku was during CoM. He can use the darkness but he doesn't really have control of it because he fears it and ultimately rejects it but is overwhelmed by it. Riku fears the darkness at the beginning of CoM but he accepts it an ultimately masters it. The only other person in the series who seems to have truly mastered the Darkness is Master Xehanort himself.
Thus instead of being more like Terra, Riku is more like MX but not corrupted by his power. Terra is the wholesome, powerful, but naive hero that was betrayed by someone he had blind faith in, thus he is more like Sora.
Plus, while Terra fueled the desire, it was originally the story about the "kid who traveled to other worlds" (MX?) that sparked Riku's wanderlust.