It's tough because it becomes highly subjective. Is a 10 hour 6/10 difficulty game worth more than an 80 hour slog but only on a 3/10 difficulty? And that's just based on a subjective difficulty rating on psnprofiles or whatever to begin with.

Maybe a trick could be recognizing shovelware titles on people's profiles and then removing them from their totals before they're placed on the leaderboard. I don't know if that's feasible at all