It would totally suck to be any of the NPCs in an MMO. You're doomed to just stand in one spot for your entire life, not even allowed to turn in place in most cases, doomed to forever stare at the same patch of dirt/same wall/same corner until someone activates a quest that ends your miserable life for a few short minutes or until the servers go down.
Ditto for being an NPC in a Bethesda game. You're just walking around minding your own business, maybe talking with someone about that super powerful bad ass hero who's been wandering the land, when said hero shows up and decides he's bored, so he butchers you and your entire goddamn town for lulz before reloading a save and bringing you all back. Or, if you're REALLY unlucky, you're tied to one of the sidequests, and he ends up talking to that guy you cheated 100 gold out of in poker while looking for something to do.
Lastly, being a marine/zealot/zergling in Starcraft would blow ass. You'd have an average life expectancy of something along the lines of 2 minutes.