They almost have the same metacritic rating at the moment. 74 vs 73.
One is considered a system seller and the other is not.
My conclusion: The arbitrary quality measurement of system selling is not at 74 vs 73 but rather quality does not come into it.
Didn't know the Destiny MC was so low. I do know that Destiny kicks the shit out of Killzone SF in every single way possible aside from visuals, so metacritic once again proves to be a useless website.
Though you can't seriously tell me Killzone SF would have received the same sales and reviews if it weren't a launch title. We were desperate to play something on our shiny new boxes.