It really does irritate me that Bioware seems to posess this atitude of "simple>complex." I loved Mass Effect and DA:O. I loved their sequels too, but it nagged at me that a lot of choices, both in gameplay and story, were eliminated.
When I first played through this quest line I figured I might have been able to change things if I just killed or arrested the elf earlier, especially since I found a trunk full of women's clothes in his mansion after I let him go. But then after I reached the actual killer it turns out he's just another of the apparent thousands of horrible blood mages who is just a bit sick in the head. (Btw, can anyone tell me why blood magic is some terrible forbidden art that only a few are supposed to practice, yet everyone and their mom uses it as a first response to the slightest thing?)
The other thing that kind of bugged me about this is the lack of drastic response from Hawke. I mean, he kills people in lots of 20 and it doesn't bother him at all, but there's nothing special about when he kills the serial killer. No fatality animations like the first game, no "Hawke smash!" cutscene where he chops or explodes the guy into tiny pieces. I understand that if they made every kill unique it would take forever and be ludicrously implausible, but I personally thought that such an obviously important fight to Hawke would warrant at least a bit more emotion and/or brutality from him when he wins. If I was in Hawke's position and possessed his abilities, there wouldn't be enough of that psychopath to fit in a thimble by the time I was done with him.