Rainbows and Emeralds!

[Boomstick]

I don't know, Grammer.  He's extremely talented in magic and in Quidditch.  And he has tons more friends than enemies.

[Grammer]

No, he's not extremely talented in magic, he's got a knack for combat magic, which is natural given what he tends to be mixed up in. You are clearly shown that the magics he masters he has to work for. He don't get any freebies.

He does not have that many friends, either. He's got a few, close friends and they're his friends for obvious reasons. And it's not like they worship him or anything. Enemies? Got no enemies at all...

Mary Sue definitions can be applied to anything. That does not mean they should be. I would not call Harry Potter a Marty Stu, as he is a developed, accomplished character (who happens to be a bit stupid). If you look at the list of Mary Sue traits, you will find that very few of them really fit him.