Alright, I'm up for some debate. COUNTOFF!
Isaac - Pretty damn silent throughout the first game till the second and third. The second game was an insult in his characterization since he was a boring hero. By the third game, though, he gets more interesting despite his short time on the spotlight.
Garet - He just sticks with you and remains mostly dumb during the two games. The third game gave him more justice, though, but it changed him quite a lot.
Ivan - Hurray, we actually got somebody interesting! Unfortunately, without all that prophecy talk, he's a bit shallow otherwise.
Mia - The only thing that motivated her to join the group was pursuing her evil cousin, and that's it. Notice how she loses overall speaking importance in the second game?
Felix - He was actually pretty damn awesome when you found out about his motives in the second game. Putting the ball of muteness into his mouth didn't cause much damage to his character development.
Jenna - Thankfully, she shared some good traits with her brother, but I don't think it was enough. That small IsaacXJenna hint could've been more fleshed out when they actually met again.
Sheba - Way more interesting that freaking Ivan, for sure. You're saying we DID get to know her? Sorry, that's not true. She fell from the sky (for a reason, as you say). But even so, she herself doesn't know anything about her past or where she came from. There's just a lot of theories revolving around Sheba that fans make up, but none of them are in-game. For now, she fell from the moon.
Piers - Truthfully, Piers seemed like a random character just like Mia, but he does flesh out quite a bit. His arc really helped him.
Matthew - Guy speaks curses! A bit better than his dad unless he's given a voice and a personality (if he goes through the same thing like Isaac).
Tyrell - Again, he's better in personality that his dad. Don't you change, little Tyrell.
Karis - Pretty likeable too. Ivan can learn four or thirteen things from his daughter.
Rief - I just like this guy. Whatever Mia could've gotten in personality was deposited into Rief.
Amiti - The resident-random Piers character of DD. Guy really likes to talk a lot after getting him, and it shows how there's story.
Sveta - Probably the best developed character with a huge potential ahead of her. Unfortunately, the ending of DD kind of makes me think she won't appear.
Eoleo - Combo breaker. The guy barely had any development besides you-know-who kicking the bucket, but his previous appearance was interesting. At least he was the last person.
Himi - Okay, seriously, this is just insulting after Eoleo. She's just a living plot coupon with no character development whatsoever. That Third Eye is probably the character, not her. She's an awesome playable character during battles, though.
In short, pre-DD had a lot of stuff in the main story yet it disregarded many characters. DD, meanwhile, did an average job at fleshing out the characters, but it was really a brief, easy experience.
