In some games that issue doesn't matter, and the player doesn't really miss not having a defined character, but with the plot of BD revolving around the soul forging of two seriously different people it seems a crippling handicap to the writing.
What do other players prefer?
It wasn't until I went back and played DD a little bit again, just for giggles, that I really missed hearing my character say anything in BD. (I didn't realize how much I liked that little level-up "brilliant!")
Now that I stop to think about it, I realize that 90% of the definition of any game character, to me, is always in my own head... but that my BD character is really less well-defined than most. For starters I don't like her body (I might have a few choice words to say about muscle and weight distribution on female bodies, but that's really so immaterial to the gameplay that it's not worth it and anyway at least in BD the women aren't 100% T&A, which puts them ahead of most) and, I realize now, the fact that I've never heard her speak leaves a bigger impact on me than I thought. I really felt that my DD character was a bit of a rogue who could really handle her bow, and that her adventures across Rivellon were just that: adventures. I don't feel much of anything about my BD character except that in team with the Death Knight, she's half of a killing machine. In fact, even though as a playing character I have more attachment to my hero, I think I have more of a personality attachment to my Death Knight. I mean, at least he has one...
It's all right too, I guess, but when I really put some thought into it, as I am now, I realize that this might be the source of my disconnect with BD. I was unemployed the summer I had DD, and spent ten hours at a time running through Rivellon... even though I could put the same time into BD now, I don't. I get tired of it after about two hours, and put it away for another day. It's not that BD is a bad game by any stratch of the imagination, but somehow it has failed to captivate me utterly, and I'm thinking that the characterization thing might just be why.
