Veteran game design Ernest Adams lists some of his favorite examples of bad game design.
Here, he quotes an example provided by Kris Kelly:
Kris: “I can only think of one occurrence of this, but I’m sure it happens in other games. In Neverwinter Nights 2, there’s a large battle involving fire giants and a red dragon. You are expected to fight on the side of one or the other but I, being a sneaky type, decided to start the battle on the side of the red dragon and then sneak out while he was fighting the giants and raid his lair.
“I wander over to his abode, loot sack at the ready, only to be confronted by a fully-healed un-harrassed-by-giants red dragon who is hell bent on fighting me, I beat him up a bit (and he reciprocates), then decide to go back to the giant fight (because it was easier) and there he is again, fighting the giants and fully healed once more.”
Look: a dragon is either guarding its lair or it’s fighting giants somewhere else. Not both. Clearly the designers implemented two dragons and led the player to believe they were both the same. Not fair and not fun.
– Ernest Adams @ Gamasutra