The fact that everyone has different characters that they love and/or hate suggests that the devs did a pretty good job.

The writing isn't stellar, but there's a wide range of character types, and one person's favorite is another's leaat. For me, Lae'zel and Astarion are insufferable (Lae'zel a little less so, but still annoying). But those are favorites of other people, so they're presumably not objectively bad, it's just a matter of taste.

My only wish is that there were one or two more, or at least that the others were introduced earlier in the game (hell no, I'm not changing my entire party dynamic in Act 3).