Bull's very funny with Blackwall ("we could fight crime!"), and the funniest interaction ever for me is the one where Bull is longingly describing missing bananas (rather suggestively, hee!) and at a certain point, Blackwall just wryly says he hopes Bull is still talking about the fruit. It's so funny.
Meanwhile, I was with Cassandra. To be honest, I had a really tough time forgiving Blackwall at all.
I think he's really well-written, because in the beginning I found him honestly rather too fawning, too all-of-a-sudden "you're amazing! the Inquisition is awesome!" to the extent that it actually made me kind of uncomfortable. But then it made perfect sense once I realized that he was desperate to redeem himself and to reinvent himself. To be the man who saved the dog instead of doing nothing and watching it die.
I did end up giving him a chance to redeem himself, but I was angry (and this definitely came out in my Quizzie #1), and I loved that we were really allowed to express our disappointment or betrayal. My Quizzie yelled at him big time in that jail cell. What he did was absolutely heinous, and it wasn't even a case of temporary insanity (like with Sten in DAO). He could have stopped it once he realized kids and civilians were involved. He didn't. Then he ran away and let his men suffer the consequences (even if I blame them as well because killing a child in cold blood? come on, orders or no orders, no way they thought that was okay...).
It's not the assassin thing for me so much as Blackwall's actions toward the family, and subsequent cowardice. (I mean, I'm not happy with the assassin thing anyway, but let's face it, we become friends with Zevran in DAO and he's quite cheerful about the job, so I don't want to be a total hypocrite.)
But I also really disliked that -- beyond all that -- he chose to impersonate a Grey Warden. After DAO that felt like a sacrilege. He didn't undergo the Joining, he didn't suffer the torment of the Calling, he was wearing a mantle he hadn't earned, and it was pretty gross once his crimes were revealed. My first Quizzie had exiled the GWs, ironically only saving Blackwall as she had "never doubted" him, so to find out that he was a liar was a big deal to me.
I didn't find myself thawing toward Blackwall again until "Trespasser." He had really worked to try to reinvent himself, he had joined the Grey Wardens and survived the Joining, and had tried to become the man he had pretended to be. He'd spent the time saving many lives and risking his own. So while I never quite forgave him, I was okay with him in the very end.