Yes. Keep in mind, though, that this is most because DE3 is directly copying sources which were fairly good.
Well, neither Tong nor the player character were very original, of course, but they were both realistic enough, and had identities that came across pretty clearly. That's actually a big step up over DE's cartoon characters and DE2's faceless nobodies. Here's a test for whether a character has been well defined: can you imagine them in a variety of different contexts outside the one you first saw them in? Do they lose any distinciveness when you imagine them that way? I think the characters we saw do fairly well on that test.
Yes. Again, dialogue needs to do more than just serve the story. Dialogue in any medium should be interesting enough to listen to on its own, without needing to know the details of the story. In high art, it also has to embody a worldview; it has to have a perspective on that world and clear ideas about it, and it has to be original (the hardest one, but the most important: if you can't write something that no one has ever written before, why are you bothering?)
The dialogue I heard in those videos sounded artificial, sounded very similar to things I've heard many times before, and wasn't really interesting enough that I would want to listen to a bunch of it outside the game. DE had some pretty interesting conversations about transhumanism, politics, and other subjects. Still, it was far better than DE2, where the gist of typical conversations was: "Hi, I'm the head of a huge corporation, and I just happened to be standing on this street corner doing nothing. Thanks for coming up to talk to me. I'm feuding with another giant corporation. I've never met you, but I feel like hiring you as an assassin, because you look tough. Kill their CEO and come back here for your reward."
