Terra is interesting to me for several reasons. The main reason is that when he makes mistakes he accepts responsibility for them and tries to fix them. Despite the fact that the darkness is growing in him, he refuses to accept the fact that it could control him or that he can control it entirely. Based on his upbringing and the values instilled within him, he keeps trying to move forward. He always tries to do the right thing but is often manipulated. He believes in people and is always willing to help out.
Sometimes this causes him trouble because he ends up doing things that can be considered wrong. Although, I feel that more often he assists in morally grey areas. He says he'll help the evil queen in Snow White's world to find someone but has not intention of actually hurting Snow White. He feels it's important to gather information about Xehanort and agrees for that reason, despite what is expected of him. He tries to follow his heart. He ends up scaring poor Snow White, finds nothing about Xehanort, and ultimately goes back to the queen and double crosses her. He feels it's more important to find Xehanort but has no problem agreeing to help if it means he can get the answers faster. He's downright practical in this regard, nor do I fault him for initially agreeing and then deciding that it's wrong and too troublesome. After guarding treasure for Hook, he realizes that he's been doing the wrong thing and goes to confront him about it. He intends go make his actions right.
In general, Terra often ends up helping people despite his internal struggles. One of my favorite instances is when he goes to the Coliseum. Hades tries to control him, but Terra chooses to fight on his own strength. He even ends up saving Zack as he ends up controlled by darkness. He breaks the darkness control on Zack. This is the second thing I like about him, he always tries to help out people regardless of what it costs him. He doesn't need a reason to help people. He just does. It's the right thing to do.
Sadly, despite Terra's abilities to help others, he is not able to break from the darkness. I love that he keeps trying though. He keeps moving forward trying to keep his head high and to conquer the darkness within him. He gets frustrated, he misunderstands his friends, and he wants nothing more than to honor his family and achieve his dreams. When he makes a mistake he internalizes it thinks about it, keeps it at heart, and tries to do better next time. I find this particularly wonderful because he doesn't always get it right, but his heart is in the right place.
I also like Terra because everything he does is for his friends, family, and dream. He goes on his journey to prove to Eraqus that he is worthy of respect and holding the Keyblade. He wants to prove that he hasn't let everyone down and that the darkness does not control him. He wants to achieve his dream and he will take the steps he needs to achieve it. He realizes that it's not so easy as wishing, it's about making those dreams come true and that means working for it.