Alright, I'm just going to come right out and say it:

I think Mary Sue's are a much too vilified form of expression. After all, true art is not written to please anyone but yourself. And if it pleases you to make a perfect world where everything is wonderful and lovely and there's not a flaw around, well? You should do it and be comfortable with the fact that it does not mean there is anything wrong with you. True, it may be boring to read about somebody else's idea of perfection and it's very possible that nobody will like it but you. But this is, as they say, fanfiction. It's a hobby. It's your art. Just try not to get too angry when it's criticized. In fact, use the criticism to become a better author. (Pretend it's Severus Snape reading your fanfic, cause you just know he'd have a few scathing things to say no matter who you are.)