Wow. I found this equally disturbing and intriguing. I was sickened by some of the characters but couldn't stop reading to find out what they were going to do next. The lines between good and bad were so blurred that I had no idea how I wanted the story to end.
And about that ending: I thought Vivian offing herself was slightly convenient for Archer not having to be held accountable for his actions. I was somewhat appeased by him spending that much time in the care facility - hopefully he would get some help, because I was NOT convinced he would not consider murdering again. He just seemed to show so little remorse for what he had done.
Evan was awesome - so loyal, though even he had an evil streak for covering up for Archer (and perhaps setting Vivian up). I personally would be fucking terrified of starting a relationship with someone like Archer.