What you like about Mario

[Gors]

The thing is that Mario isn't more about the character 'Mario'; as Zac said he is literally a 'good avatar' and the personification of a good person, and this 'blankness' allowed him to have games of many genres

Thus, you can relate to the game because you already know him, even if you don't like, for example, RPGs. I don't really like RPGs but I remember being interested in Mario & Luigi because.... it was Mario

Sure, the game (and if it's a RPG, plot) is more important than a name, but the fact that Mario is in the title and there is kind of a visual association gives us the "proof" that it's Nintendo's top stuff. Of course, that is not 100% true, but putting a familiar face in the games helps increase acceptance to an extent