I suppose my characters could be seen as something in the vein of "Mary-Sue"s... I tend to see them as I do all the characters, but particularly the protagonists, in the stories, plays, and so forth that I write... I can certainly relate to them... They are aspects of myself fleshed out, and thus tend to have similar flaws to ones I know I manifest myself from time to time... some of them have tempers - something I've known about me since I was about 5 and over the years have had good years and bad years as I learn to control it - for example. Others have other flaws but they're all things that I see in myself, like reflections in a funhouse mirror twisted so they are me, and yet someone new too... I generally try to get into their mind, see things from their point of view, feel what they feel, sense what they sense, know what they're thinking each moment... which is rather disorienting and yet quite informative when I try, from time to time, playing a female character. It's interesting to see how each character reflects me, echos me, and yet grows apart and lives a life of it's own from the seeds of me planted in the ground of a different background and grown through the course of adventures and so on.
My characters also tend to be intelligent, rational minded type tacticians, like an earlier poster mentioned - which *is*, admittedly, an idealized version of the way I see myself. They are generally erudite to a greater or lesser extent, and have seemed to often wind up the leader of the group. I don't mind this role, but I also don't want to hog the center of attention... let other people lead sometimes. I remember several campaigns with a group where I tend to lead where I made a conscious effort to try to fade into the background and was unsuccessful... I'm not sure what that says about me really... maybe has something to do with the fact that my BA's in Theatre Arts, but that's what I've noticed. What specifically I've "learned" from roleplaying D&D and not from from reading, reflection, and personal experience I'm not entirely sure, but I'm sure there have been things. And I don't think, as another poster said:
After 27+ years: nothing. Please. Anyone who thinks otherwise needs professional help.
Anytime you learn something about yourself, no matter the source or situation, it's a good thing I think. Self knowledge is one of the most important things in order to succeed in life. To quote Sun Tzu from his "Art of War", "Hence the saying: If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle."