The Good Slytherin?

I just posted this on a list as a comment but it struck me as something I'd throw out and see what other people thought. Some may know I've always been very wary of the idea of "The Good Slytherin," that mythical character that's supposed to be introduced and so redeem the house in canon, but it still seems to be a favorite fandom idea. (Isn't Phineas awesome enough??!) This came up in a discussion of Slughorn as such. Now, Slughorn obviously is not a Death Eater and he's never sung 'Weasley is Our King' so I guess that puts him above every other Slytherin in canon so far, but still, ( Is he really good? )