In our Northern Reaches campaign we have been playing double rolled damage on a critical hit. That was an extension of how I played AD&D and AD&D 2nd Ed. back in the day. If you rolled snake-eyes for your dmg that was just too bad.
[On a critical miss I have the players must roll on a custom table to see what happens. Formerly, I had monsters roll double damage but it just killed way too many PCs so I dropped the critical hit/miss option for them]
I'm curious, how do you play critical hits/misses in your old school game?