I actually found asterion more interesting after it became apparent he did not really have a hidden soft side. That he is a through and through sociopath who, if one uses detect thoughts, is trying to appear as if he has standards and banking hard on the victim angle to manipulate the pc. Adds a bit of unpredictability to the party, teaches me I cannot take everything the companions say at face value.
Same here.
I realise it might not necessarily be a common opinion, but I find it quite refreshing. In an age where far too many villains need to be morally grey and relatable it's refreshing to just have a companion who is (or at least appears to be) irredeemably evil.