I've played it both ways with Gratiana due to not really make my mind up about her past evils being irredeemable vs. whether she really has changed and is atoning for her sins (which, as Levianne points out, is indeed the case). Lovis from DKS was different: this time I was all set to forgive his past having forgotten his true nature, but it didn't take long to realise that he was still absolutely unrepentant about what he'd done.
I'm also really bad at RPing other personalities, though: once in a while, just out of curiosity, I try to see what it's like playing as an evil character but I just can't do it. One notable attempt went from being an evil raider type in Fallout to being a bit nasty to morally questionable to more sort of neutral to surly to a bit sarcastic but she didn't really mean it, all in a fairly short space of time. I've seen people say things like "who doesn't like to go and massacre an entire town" and I'm left thinking, "well, me, actually." They may just be computer-controlled characters but it still makes me feel bad if they "die"!
