Vance was interesting through his menacing personality and vampire characteristics. Simon was mostly mysterious as the angel trapped within him wasn't revealed until towards the end of the story. I read half the book thinking patient 66 was actually the evil manifestation of Simon, spawn from within him, somehow.
They all had flaws and insecurities in regards to their paranormal abilities and it took their combined efforts to not perceive them as lessening and evil. Of course, their perfect coming together, without any jealousy or any other problems, seemed a bit forced. But in the end, I was glad they survived the horror of the imprisonment (albeit needing years of therapy) and had their happily ever after.