Keeper of the Superfluous Es!

To preface, let me say that I generally read fic because I'm interested in relationships and character dynamics. Therefore the weaknesses I like to see are related to emotional abilities. Substance addiction is both physical and psychological, and while it can have a significant effect on a relationship, it's almost more of an external influence. I prefer weakensses that are shortcomings in the emotional maturity necessary for a relationship--lack of trust, communication issues, family, how does one cope with change, etc. True addiction is all about the addict, all the time (ask anyone who's dated or been married to an addict--when they're using you worry about when they're going to stop, when they're not using you worry about when they're going to start). I want to read a story that's about two people coping simultaneously with both of their issues and working to overcome what they can.

As far as it being Mary Sue-ish, I think of a Mary Sue as a character that the author would want to be, and giving that character the author's addictions takes them one step closer. I don't think it is a Mary Sue, just shades of.