With Laurell K. Hamilton's new book, Bullet coming out next week, I thought it prudent to give authors, new and published, a little assistance in avoiding the deep, dark pit of Mary-Sue-ism.
For those who don't know what a Mary-Sue (or a Gary-Stu/Marty-Stu) is, here's a definition:
A Mary Sue is a pet character that the author exempts from realism and/or rules that otherwise govern a fictional world. The more that the author exalts this "darling" at the expense of the rest of the story, the more of a Mary Sue the character becomes. Mary Sue is impervious to failure and resistant to all in-story attempts at criticism and humiliation; any attempt at an external critique usually provokes an authorial temper tantrum. With a preference for style over substance, attitude over empathy, and romantic relationships above all others, the Mary Sue is nevertheless a popular character type due to her function as cheap wish-fulfillment. (PPC Wiki)
So, if you want to know if the protagonist you've worked long and hard on is a Mary-Sue, go to The Original Fiction Mary-Sue Litmus Test. Answer the questions and find out if your character is doomed. I got a borderline Sue for one of my characters, so I'll have to work on that.
As an added bonus, you can go to TV Tropes. "Tropes are storytelling devices and conventions that a writer can reasonably rely on as being present in the audience members' minds and expectations."
(There are no official reviews of Bullet, but if you're canny enough to go to Amazon.com, you might find something of a... bullet point synopsis. If you don't want to know anything about it, don't read the discussion. Oops. Did I give it away? My bad...)