We chat about videogames and videogame accessories.

I think he meant they were a good example of a blank slate character that still expresses some kind of personality?
I'd say in that regard they are definitely more successful than Mario or Link (although he's better at it in some games depending on the art style) but wouldn't go so far as to say Shepard was a "good character"

Well, yes, that. I kinda thought it was obvious from context but I guess not. So, yes, what I meant was that Shepard has the same function as Mario in terms of "immersion", but pulled it off much better simply by virtue of being allowed to speak and have a personality. Yes, this personality is very mix-and-match, but at least it's there.

Note: I happen to like my particular iteration of Shepard very much, even if a lot of the details of the character are mostly in my head.