There's nothing wrong with creating a character as a wish-fulfillment device. I'm guilty of doing this myself. Way back in the dark ages of 2003, I wrote a game about a laid-back surfer with a very sunny disposition, who was allergic to work and only cared about the next wave. I am nothing like this character. I live for the city and am not a huge fan of beaches. But at the time, I was working in a corporate cubicle factory, sitting under florescent lights all day, doing really boring corporate things. I was envisioning the prospect of spending the rest of my life like that and it was terrifying. So I came up with this character as a way to escape. I suppose the character could be considered a Mary Sue (a Marty Sue?) to a degree, taken in that context.
But I think what makes a wish-fulfillment character a Mary Sue is when the wish-fulfillment is so generic and boring that is ceases to be engaging to anybody but the creator. Just wanting to be liked by others and good at stuff is a good wish to have, but is that engaging? In terms of adventure games, I always felt that Brian Basco from Runaway fit this description. He was just so banally nice and pleasant. Everybody liked him. He magically had the knowledge to solve any situation he was in ("Oh no, I'm at the edge of a sheer cliff face. Good thing my uncle taught me how to rockclimb when I was a kid!"). Hot chicks fell in love with him for no reason other than he was the "hero." There were no major flaws to speak of, nothing to make him interesting. Admittedly, I haven't played the other games in the series but he was definitely a Marty Sue in the first installment.
Of course, by the same token, George Stobbard of Broken Sword fits the same description, but I still enjoy playing the games he is in because the writing is so good (disclaimer: I haven't played BS4). So as with anything, it boils down to the talent of the creator. Nothing is wrong with a wish-fulfillment character, as long as the character is interesting enough to others.
But I think what makes a wish-fulfillment character a Mary Sue is when the wish-fulfillment is so generic and boring that is ceases to be engaging to anybody but the creator. Just wanting to be liked by others and good at stuff is a good wish to have, but is that engaging? In terms of adventure games, I always felt that Brian Basco from Runaway fit this description. He was just so banally nice and pleasant. Everybody liked him. He magically had the knowledge to solve any situation he was in ("Oh no, I'm at the edge of a sheer cliff face. Good thing my uncle taught me how to rockclimb when I was a kid!"). Hot chicks fell in love with him for no reason other than he was the "hero." There were no major flaws to speak of, nothing to make him interesting. Admittedly, I haven't played the other games in the series but he was definitely a Marty Sue in the first installment.
Of course, by the same token, George Stobbard of Broken Sword fits the same description, but I still enjoy playing the games he is in because the writing is so good (disclaimer: I haven't played BS4). So as with anything, it boils down to the talent of the creator. Nothing is wrong with a wish-fulfillment character, as long as the character is interesting enough to others.